The following combination of characteristics distinguish Poa from other grass genera in Mexico, and in most of the world. The plants are annual or perennial, and rarely exceed 1 m in culm length. The culms are simple, hollow, and unbranched above the base. Plants sometimes have rhizomes, but only infrequently are weakly stoloniferous. The leaves are unusual in that the upper culm leaf sheath margins are fused over 5 to 100%; the blades are abaxially keeled and typically have only two channels on the adaxial surface (sometimes obscure), one on either side of the midvein, that are lined with thin-walled bulliform cells that collapse to fold the blade in dry conditions; and the blade apex is typically prow-shaped to some degree (in these features they are like Glyceria). The vegetative structures lack long pilose hairs and microhairs. Like all Pooideae, the blades lack Kranz anatomy. Ligules are scareous (white) to hyaline, without apical or lateral cilia (sometimes minutely ciliolate). The inflorescences are simple, paniculate, and terminal. Poa spikelets are unspecialized, usually between 2.5 and 8 mm long, normally with 2 and 5 florets (sometimes 1 in Poa gymnantha), and disarticulate above the glumes and between the florets. The spikelets and florets are laterally compressed and lack awns. The florets are all alike, but are reduced upward and the uppermost is often rudimentary. The glumes are persistent, typically the lower one is 1 or 3-veined; the upper 3-veined, slightly narrower and thinner than the lemmas, generally slightly shorter than the lower floret (longer in Poa thomasii and Poa calycina; the lower glume can be quite short in Poa seleri), and are often somewhat unequal. The rachilla is terete, usually at least 0.4 mm long between florets and is prolonged beyond the uppermost, well developed floret (except in Poa calycina where the internode is 0.2–0.3 mm long and sometimes is not prolonged above the 2^nd floret). The lemmas are usually distinctly keeled (except Poa secunda), and commonly are pubescent with hairs on the lemma and/or the callus. The lemma apex and margins are variously narrowly to broadly scareous-hyaline. The lemmas are typically 5-veined but this varies from 3 (Poa calycina) to 9 (Poa mulleri). The palea surface is thinly herbaceous (unlike Koeleria, in which it is hyaline). The callus of the lemma is terete or slightly pinched dorsally, blunt, and fairly indistinct in its transition to the lemma (unlike Festuca and Schedonorus, which have a dorsally compressed rachilla and a somewhat thick, annulated, glabrous callus, that is sometimes angled downward). The callus typically has an isolated dorsal tuft of woolly hairs called a web, but the callus is glabrous in some taxa (In Poa secunda the callus lacks a web but sometimes has a line of short hairs < 0.2 mm long or crown on the callus around the base of the lemma). The lodicules are two in number, usually ovate to lanceolate with a lateral lobe, without distinct vascularization, glabrous, and the upper portion is hyaline. Anthers are 3 in number (sometimes 1 or 2 in Poa bigelovii), and within pistillate flowers are typically reduced to staminodes. Ovaries are glabrous with 2 styles that are apical, approximate, plumose, and white. The caryopsis is firm (but known to contain lipid), ventrally sulcate with a short (usually less than 1/7 the grain in length) subbasal hilum, and the embryo is small (less than 1/6 the grain in length).

Chromosome base number is x = 7, of medium to medium-large size.

The genus is Worldwide but is usually not found in tropical countries without high mountains. In Mexico the genus is known from all states except Nayarit, Quintana Roo, Sinaloa, Tabasco, and Yucatan.

Species of Poa occur in cool temperate to frigid regions, cool habitats in warm temperate regions, and in dry to wet habitats.

Poa is a complex genus of more than 500 species with 23 occurring in Mexico. It is the type genus of the family Poaceae, subfamily Pooideae, supertribe Poodae, tribe Poeae, and subtribe Poinae (Soreng et al. 2011). The above synonymy for the genus is the most current available, however, two species of Aphanelytrum (and one of Festuca related to those) have not yet been formally transferred into Poa. Poa is known for great diversity in breeding systems (Anton and Connor 1995; Negritto and Anton 2000; Soreng and Keil 2003). In Mexico species may be strictly perfect flowered; gynomonoecious (spikelets with lower florets perfect and upper ones pistillate); possibly sequentially gynomonoecious (some plants shifting to producing more pistillate flowers as the season progresses); dioecious (sexual dimorphism was not evident in the Mexican species); or pistillate only. Apomictic/asexual reproduction by seed is common in some species of the genus, and is sometimes facultative (Clausen 1961, Kellogg 1987), and other times effectively obligate (Soreng and VanDevender 1989; Negritto et al. 2008). In Mexico Poa chamaeclinos and Poa gymnantha are strictly pistillate apomicts, and Poa fendleriana is pistillate and apomictic over much of its range. Poa alpina, Poa compressa, Poa pratensis, and Poa secunda are known to be facultatively apomictic elsewhere, but their breeding systems have not been studied in Mexico. Poa strictiramea is predicted to be apomictic in Mexico based on the high frequency of sterile anthers. No viviparous/bulbiferous spikelets were found among Mexican specimens. Other relevant literature on Poa includes: Soreng (1990), Gillespie and Soreng (2005), Gillespie et al. (2007, 2009), Soreng et al. (2009, 2010), Refulio-Rodríguez et al. (2012) ―molecular data; Soreng (2005) ―chromosome counts; and Tzvelev (1976), Zhu et al. (2006), Soreng (2007), Giussani et al. (2012) ―floristic accounts.

Europe, in alpibus Lapponicis, Helveticis (lectotype: LINN-87.2!, designated by Soreng 2000: 254).

Uralepis mutica E. Fourn., Mexic. Pl. 2: 110. 1886. Type: Mexico, Liebmann Gramineae No. 611 (holotype: C, photo US; isotype: US!, right hand culm ex C present in photo taken by A.S.Hitchcock).

Poa violascens Phil. Linnaea 29(1): 100. 1858. nom. illeg. hom., non. Cheval. 1827. Type: Chile, Cerca de Arauco, C. Gay Herb. Chil. 164 (holotype: SGO-PHIL-413!; isotype: SGO-45741!).

Hermaphroditic. Perennials; tufted, tufts dense, fairly narrow to medium girth, low (mostly less than 8 cm tall), dark green to slightly bluish-green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), without cataphyllous shoots, sterile shoots more numerous than flowering shoots. Culms 10–40 cm tall, erect, sometimes slightly geniculate at base, leaves mostly basal, terete, smooth; nodes 1–2, 1 usually exerted. Leaves mostly basal; leaf sheaths terete, smooth, glabrous; butt sheaths persistent, papery, proximal sheaths densely overlapping, persistent; flag leaf sheaths 4–8 cm long, margins fused ca. 12–29% the length, much longer than its blade; collars smooth, glabrous; ligules of upper cauline leaves to 4(–5) mm long, milky white, abaxially smooth, glabrous, apices obtuse, of sterile shoots 1–2(–3) mm long; blades of cauline leaves 1–5(–12) cm long, 2–4.5 mm wide, flat, moderately thick, soft, straight, mostly basal, smooth or margins lightly scabrous, broadly prow-tipped; upper culm blades reduced in length; flag leaf blades ca. 1 cm long; sterile shoot blades widely spreading, persisting through the season. Panicles 2–6(–8) cm long, erect, open or loosely contracted at maturity, pyramidal to ovoid, fairly congested, proximal internode 0.6–1(–1.5) cm long; rachis with 1–2 branches per node; primary branches ascending to spreading, straight, to divaricating in flower, terete, smooth or very lightly scabrous, rarely moderately densely scabrous all around; pedicels divaricately spreading, lateral pedicels 1/5–1/2 the spikelet in length, smooth or sparsely to moderately scabrous; longest branches 1–3(–4) cm. Spikelets 3.9–6.2 mm long, 1.5–2.5 × long as wide, ovate, laterally compressed, but plump; florets 3–7, rarely bulbous basally and leaf-like distally (in high arctic), hermaphroditic; rachilla internodes terete, 0.5–0.8 mm long, smooth, glabrous or sparsely softly puberulent to short villous; glumes broadly lanceolate to narrowly ovate, distinctly keeled, keels lightly scabrous, acute, lower glumes 3-veined; upper glumes shorter than or subequaling lowest lemma, 3-veined; calluses glabrous; lemmas 3–5 mm long, broadly lanceolate, distinctly keeled, keels and marginal veins short to long villous, between veins sparsely to moderately short villous, intermediate veins moderately prominent, apices acute to obtuse; paleas softly puberulent to short villous over the keels for most of the length, apices scabrous. Flowers chasmogamous; lodicules 0.65–0.75 mm long, broadly lanceolate to ovate, with a short lateral lobe; anthers 1.3–2.3 mm long. Caryopses 1.9–2.2 mm long, elliptical in side-view, sulcus shallow, brown, hilum 0.25 mm long, round to oval, grain adherent to the palea. {North American counts}. 2n = 28, 32, 33, 34, 35, 39, 40+I, 42, ca. 48, 56.

The species is circumboreal and in North America it ranges from Canada, Greenland, USA, south to Mexico. It is known only from the type collection and the location in Mexico is unknown.

The species is found in disturbed sites in boreal forests, subalpine to low alpine meadows, and rocky slopes, on calcareous to acidic substrates.

The species is common in North America and rare (if extant) in Mexico.

Poa alpina was first reported for Mexico by Hitchcock (1935) and was accepted by Hultén and Fries (1986), Beetle (1977), and Soreng et al. (2003), based solely on the identity of the type specimen of Uralepis mutica which Fournier (1886) described in his Mexicanas plantas as “Absque loco". The holotype was annotated as “Uralepis mutica Fournier" by Fournier, and “Liebm. Pl. México No. 6233" was added to the original ticket at C. In a United States National Herbarium author’s proof copy of Hitchcock (1913), Agnes Chase penciled in a note that the type was determined by A.S. Hitchcock as Poa alpina, “but that not in hb. from south of Co[lorado], Verify". The southernmost collections in the United States are from the Sangre de Cristo Range of the Rocky Mountains in northern New Mexico [UNM: Mora and Santa Fe cos.; NMC Taos Co.; in Soreng (2007) the map only shows Taos Co. in New Mexico]. The Liebmann specimen might have been collected in the Rocky Mountains in the former Mexican Territory (New Mexico became a territory of the United States in 1848), but we have no evidence of Liebmann collecting there (neither K. Allred nor R.W. Spellenberg have knowledge of Liebmann having collected in New Mexico, pers. comm., 2011). Furthermore, the taxon is rare in New Mexico, having been recorded for the state in only three localities, all post 1980. F.M. Liebmann (b.1813, d. 1856), Danish botanist (main herbarium at C, ca. 90000 specimens) is well known to have collected extensively in central and southern Mexico in Oaxaca, Puebla, and Veracruz between 1841 and 1843 (McVaugh 1987). A few of his collections recorded from other years in Tropicos are likely transcriptional errors (Missouri Botanical Gardens taxonomic database: http://www.tropicos.org/Home.aspx, fide Gerrit Davidse 2012). McVaugh only cites the 1841 to 1843 for Mexican collections. A brief on-line biography (http://www.nathimus.ku.dk/bot/liebmann.htm) of Liebmann does not give any suggestion that he traveled in or collected in the United States, indicating that he traveled to Cuba and Mexico between 1840 and 1843. Although (Harvard University Herbaria) HUH Index to Botanists indicates he also collected in the United States (http://kiki.huh.harvard.edu/databases/botanist_search.php?mode=details&id=1049), it seems unlikely that he would have had an opportunity to collect Poa alpina in the USA without having left a substantial record of collections from the country, and such a record seems to be absent. Liebmann did collect on Pico de Orizaba in 1841, and on the highest mountain in Oaxaca, Zempoaltépetl (3397 m), in 1842 (McVaugh 1987), and these seem to be the only places in Mexico the species could have been found by Liebmann between 1841 and 1843. Liebmann nos. 603 to 610 are known to be from Orizaba, and 611 might also be from there, however his label numbers are not sequential but were added afterward to organize his collections (McVaugh 1987). The Poa alpina specimen could have come into Liebmann’s herbarium and become mixed with Mexican material by some other means. We believe the reputed coastal Arauco, Chile, origin of the type of Poa violascens Phil. resulted from a such a mistake by Philippi; see synonymy above. Liebmann also traveled in Norway and Germany and had substantial material from other botanists. Nevertheless, it is possible for a common species like Poa alpina to have become established this far south in Mexico.

Gynomonoecious. Annuals (rarely surviving for a second season); tufted, infrequently short stooling, tufts generally small, bases usually narrow, green to light green; tillers intravaginal (each subtended by a single 2-keeled, longitudinally split prophyll over 0.5 cm long), without cataphyllous shoots, most shoots eventually flowering. Culms 2–20(–45) cm tall, spreading to erect, sometimes geniculate, leafy, slender, terete, smooth; usually 1 nodes. Leaf sheaths terete or weakly compressed, smooth, glabrous; butt sheaths papery, smooth glabrous; flag leaf sheaths 1–6 cm long, margins fused ca. 33% the length; throats and collars smooth, glabrous; ligules 0.5–3(–5) mm long, decurrent, abaxially smooth, glabrous, apices obtuse to truncate; blades 1–10 cm long, 1–3(–6) mm wide, flat or weakly folded, thin, soft. smooth, margins usually slightly scabrous, broadly prow-tipped; blades all about equal in length, flag leaf blades well developed. Panicles 1–7(–10) cm long, 1.2–1.6 × long as wide, erect, open, pyramidal to rhomboid, moderately congested to sparse; rachis with 1–2(–3) branches per node; primary branches ascending to spreading or reflexed, straight, terete or sulcate, smooth; lateral pedicels less than 1/3 the spikelet in length, smooth; longest branches 2–4(–5) cm, spikelets crowded or loosely arranged. Spikelets 3–5 mm long, ovate, laterally compressed; not bulbiferous; florets 2–6, proximal hermaphroditic, distal often pistillate; rachilla internodes terete, smooth, glabrous, more or less concealed or exposed, distal internode less than 1/2(–3/4) length of distal lemma; glumes unequal, smooth, distinctly keeled, keels smooth; apex acuminate to acute or obtuse, sharp pointed or slightly blunt; lower glumes 1–2.2 mm long, 1-veined, narrowly lanceolate, often slightly sickle shaped, or subulate, apex acute; upper glumes 1.5–2.5 mm long, shorter than or subequaling lowest lemma, 3-veined, lanceolate to oblanceolate, apex obtuse to acute; calluses glabrous; lemmas 2.2–3.3(–4) mm long, broadly lanceolate, green to light green, sometimes slightly anthocyanic, distinctly keeled, smooth throughout, keels, marginal, and usually intermediate veins moderately to densely crisply puberulent to long villous, rarely glabrous throughout, between veins glabrous, intermediate veins prominent, margins and edges smooth, apices obtuse to acute; paleas keels smooth, short to long villous, rarely glabrous over the keels. Flowers cleistogamous to chasmogamous; lodicules 0.45–0.5 mm long, broadly lanceolate to ovate, with 1 (rarely 2) short lateral lobe(s); anthers 0.6–1.1 mm long, oblong prior to dehiscence, often vestigial in distal flowers of a spikelet. Caryopses 1.6–1.8 mm long, elliptical in side-view, subcylindrical in cross-section, light brown, sulcus almost flat, hilum 0.15 mm long, oval, grain free or adherent to the palea. 2n = 28.

The species is distributed Worldwide, primarily in temperate and subtropical regions. In Mexico it is recorded from all states, except Campeche, Nayarit, Quintana Roo, Sinaloa, Tabasco, and Yucatán.

The species is a gynomonoecious, ruderal annual (infrequently a short-lived perennial), and is found in waste ground, lawns, gardens, trails, sidewalks, roadsides, fields ranging from sea level to over 4500 m. The species can potentially flower throughout the year.

Mexico. Aguascalientes: Municipio Aguascalientes, Aguascalientes, 18 Sep 1978, J.A.Zamarripa-D. (MEXU). Baja California: Guadalupe Island, North Twin Cañon, 50 m, 24 Apr 1958, R.Moran 6622 (US). Baja California Sur: reported by Espejo Serna and Lopez Ferrari (2000). Chiapas: Escuintla, 3 Oct 1936, E.Matuda 312 (US). Chihuahua: vic. of Chihuahua, 1300 m, 27 Apr 1908, E.Palmer 28 (US). Coahuila: Saltillo, Apr 1898, E.Palmer 6 (US). Colima: reported by Espejo Serna and Lopez Ferrari (2000). Durango: Durango, Apr 1896, E.Palmer 97 (TAES, US). Distrito Federal: Azcapotzalco, 27−30 Jul 1910, A.S.Hitchcock 5929 (US). Guanajuato: Municipio Cortazar, Ejido del Rancho del la Gavia, 2330 m, 9 Oct 1996, s. collector (MEXU). Guerrero: Municipio Tlacotepec, Cerro Teotepec, 3350 m, 5 Dec 1963, J.Rzedowski 18145 (MEXU, MSC). Municipio General Heliodoro Castillo, El Jilguero, 2600 m, 30 Oct 1998, N.Diego 8146, B.Ludlow & A.Acosta (MEXU, lemmas glabrous or nearly glabrous). Hidalgo: Pachuca, 6−7 Sep 1910, A.S.Hitchcock 6747 (US). Jalisco: Mt. Nevada, 23−24 Sep 1910, A.S.Hitchcock 7154 (US). Michoacán: 8−10 mi NW of Ciudad Hidalgo, 2850−3000 m, 18 Mar 1949, R.McVaugh 9902 (US). Municipio Tallpujahua, Presa Brockman, 2760 m, I.García 3603 & Y.H.-deG (MEXU, stooling form). Morelos: Morelos, El Parque, 31 Aug 1910, C.R.Orcutt 3858 (US). Mexico: woods near El Oro, 9000 ft [2745 m], 14 Sep 1901, C.G. Pringle 9589 (TAES).Ixtaccihuatl, Oct 1905, C.A.Purpus 1618 (US). Nuevo León: Cerro Potosí, 9000 ft [2745 m], 7 Jul 1963, R.L.McGregor 267, L.J.Harms, A.J.Robinson, R.del Rosario, R.Segal (US). Oaxaca: Oaxaca, 5000 ft [1525 m], 30 May 1894, C.G.Pringle 4671 (US). Puebla: Tehuacán, 9 Aug 1910, A.S.Hitchcock 6049 (US), Ixtaccihuatl S flank, in circ E of the “portal" N of La Amacuilecatl “Los Pies", 19.1543°N; 98.6307°W, 4400 m, 2 Oct 1987, R.J.Soreng 3323 & N.Soreng (US, stooling form). Querétaro: Querétaro, 24−25 Jul 1910, A.S.Hitchcock 5829 (US). San Luis Potosí: Alvarez, 28 Sep to 3 Oct 1902, E.Palmer 173 (US). Sonora: Guadalajara, Jul−Oct 1886, E.Palmer 483 (US). Tamaulipas: Reported (Espejo Serna and Lopez Ferrari 2000). Tlaxcala: Municipio A. Arista, 5 km al sur de San. Felipe Hidalgo, 3000 m, 15 Dec 1988, R.Acosta 2689 & M.Sánchez (MEXU). Veracruz: Jalapa, 4600’ [1400 m], 2−4 Sep 1910, A.S.Hitchcock 6625 (US). Zacatecas: near Plateado, 1 Sep 1897, J.N.Rose 2712 (US).

This Old World species is naturalized throughout temperate regions of the New World. The species was already widespread in Mexico by the mid-1800’s: Popocatepetl, H.G. Galeotti 5828, 5854 (US fragm. ex CAEN in 1837−1847); Orizaba, F. Müller 2094 (US fragm. ex P in the 1850’s); and San Luis Potosí, M. Virlet-d’Aoust 1372, 1394 (US fragm. ex P in 1851). Above we list a single specimen per state for this species, except when there is notable morphological variation. We cite the oldest voucher seen that came from the state. The species probably occurs sporadically in additional states and is surely in Sinaloa but without a collection. Plants from wet areas at high altitudes can perenniate by rooting at the nodes (noted in specimens cited from Michoacán and Puebla), and such forms have been called Poa annua var. reptans Hausskn. We suspect that such forms arise repeatedly in plastic response to the environmental conditions, rather than from unique genetic variation, and are not particularly useful to recognize taxonomically. A form with the lemmas and paleas glabrous or nearly glabrous occurs sporadically around the world, and has been found in Guerrero. All collections from Mexico we have seen identified as “Poa infirma" belong to Poa annua, and only one specimen was redetermined by us as Poa infirma from among hundreds of Poa annua specimens. DNA data support the hypothesis that Poa annua, a tetraploid species, arose from hybridization between two Eurasian diploid species, Poa infirma × supina Schrad. (Soreng et al. 2010). Poa infirma is a short-lived annual and Poa supina is a stoloniferous perennial. Species of this complex [Poa sect. Micrantherae Stapf; syn. Poa sect. Ochlopoa Asch. & Graebn., Ochlopoa (Asch. & Graebn.) H. Scholz.] have spikelets with perfect lower florets and pistillate upper florets, smooth branches and spikelet bracts, and soft puberulent lemma keels and marginal veins, soft puberulent palea keels, and glabrous calluses. Poa annua frequently approaches Poa infirma in form, presumably in part due to expression of particular genes, or segregation of those genes toward the parental species. This hypothesis explains the difficulty of identifying true diploid Poa infirma. In a separate review of US New World specimens previously identified as Poa annua or Poa infirma by Hildemar Scholz (B, dets. of 2007), only one specimen from Central America was identified as other than Poa annua (see Poa infirma discussion below).

Mexico, Baja California, Sierra San Pedro Mártir, E rim above Yerba Buena, 31°01'N, 115°W, 2700 m, 1 Jun 1968, R. Moran 15070 (holotype: US-259736!; isotypes: SD-69304!, TAES-16825!).

Hermaphroditic. Perennials; tufted, tufts dense, fairly narrow to medium girth and low to medium height (5–12 [–15] cm tall), pale green to bluish green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), without cataphyllous shoots, sterile shoots more numerous than flowering shoots. Culms 20–50 cm tall, erect, blades strongly reduced upward, terete, smooth; nodes 2–3, smooth, upper (0–)1–2 exerted, uppermost at mid-culm. Leaves mostly basal; leaf sheaths slightly keeled, very sparsely to moderately (rarely densely, evenly, finely scabrous; butt sheaths persisting, grayish-brown, papery, their blades disarticulating, the bases smooth, glabrous; flag leaf sheaths 8–15 cm long, margins fused 29–36% their length, (2.5–)10–16 × longer than its blade; collars vestiture like that of the sheath; ligules 0.25–0.5 mm long on basal leaves, to 0.5–1.5(–2) mm long on upper culm leaves, abaxial surface and upper margins densely scabrous, apices truncate to obtuse; blades to 10(–15) cm long, 1.5–2.75 mm wide, folded or flat, margins inrolling, moderately thick abaxially smooth or lightly scaberulous (denser apically), margins scabrous, adaxially smooth or moderately to densely scaberulous, narrowly and abruptly prow-tipped; culm blades sharply reduced upward, flag leaf blades 0.1–1.5(–4) cm long. Panicles 4–13 cm long, erect, open, pyramidal, well exerted, sparse, with 16–50 spikelets, peduncles smooth, proximal internode 1.8–3.9(–5.2) cm long, smooth; rachis with branches 2–3(–5) per node; primary branches widely spreading to reflexed, fairly strict, terete to weakly angled, smooth or sparsely scaberulous proximally, smooth or moderately (rarely densely) distally, hooks not confined to rows on angles; lateral pedicels mostly about half the spikelet length, smooth or sparsely scabrous, prickles fine; longest branches 3–7 cm, with 3–15 spikelets in the distal 1/2. Spikelets 3.75–8 mm long, lanceolate, laterally compressed not bulbiferous, pale green to strongly anthocyanic; florets (1–)2–4(–6), hermaphroditic; rachilla internodes terete, 1.25–2 mm long, smooth, glabrous; glumes, lanceolate to narrowly lanceolate unequal to subequal, shorter than the first lemma, distinctly keeled, thin, smooth or lightly scabrous distally, lateral veins and apical surfaces smooth or lightly scabrous, sharply acute; lower glumes 2.5–3 mm long, ca. 1/2 the adjacent lemma in length, 1(–3)-veined; upper glumes 2.8–3.5 mm long, 3-veined, often 2 × wider than the lower one, ca. 3/4 the adjacent lemma in length, with a broad scarious-hyaline margin; calluses glabrous or webbed, web sparse, hairs to 2 mm long, woolly; lemmas 3.2–4.2 mm long, lanceolate, 5 veined, green to strongly anthocyanic, distinctly keeled, (rarely glabrous throughout), keels to 4/5 and marginal veins to 1/2 sparsely to densely sericate, between veins glabrous or sparsely puberulent in lower 1/2, smooth except for hooks on the upper keel, intermediate veins faint, margins scarious hyaline, edges smooth or with a few fine hooks, apex acute; paleas finely and closely scabrous, glabrous or in some plants medially sparsely softly puberulent, intercostal area glabrous or sparsely puberulent. Flowers chasmogamous; lodicules 1 mm long, lanceolate, apex obtuse, unlobed; anthers 1.7–3.2 mm long (rarely sterile, but then 1.7–1.8 mm long). Caryopses 1.9–2.3 mm long, elliptical in side-view, compressed, light honey-brown, sulcus narrow, shallow, hilum 0.25 mm long, oval, grain free from the palea. 2n = unknown.

The species is known only from Baja California and is endemic to Sierra San Pedro Mártir.

This species occurs on mountain slopes, flats, and drainages, and is associated with Salix and Populus tremuloides Michx. thickets, Quercus−Pinus jeffreyi forests, and Quercus−Pinus jeffreyi−Poa lambertiana−Abies concolor forests, and open meadows in Pinus jeffreyi Balf. forests. It is found in sandy to rocky to clay, granitic, often duff-covered soils, between 1450−2950 m. Flowering May to June.

The species is a narrow endemic and locally frequent.

Mexico. Baja California: Sierra San Pedro Mártir crest of range N of observatory, head of Cañada el Copal and S slope of Cerro Venado Blanco, 2500−2700 m, 3 Jun 1988, S.Boyd 2311, T.Ross, K.McCulloh (RSA). La Concepcíon, 31°01'N, 115°37'W, ca. 1450 m, 31 May 1968, R. Moran 15006 (SD, TAES). open W slope of Cerro 2828, ca. 31°02'N, 115°27'W, ca. 2800 m, 31 May 1968, R. Moran 15060 (BH, SD, TAES). 2 mi W of Vallecitos, 31°00'N, 115°29'W, ca. 2250 m, 2 Jun 1968, R. Moran 15083 (SD, TAES). 3 km NE of El Alto de Corona, 31°00'N, 115°41'W, ca. 2400 m, 20 Aug 1977, R. Moran 24555 (SD). W slope below summit of El Picacho, 30°59'30"N, 115°22'30"W, ca. 2950 m, 5 May 1978, R. Moran 25611 (SD, TAES). end of road into high end of northern sierra, ca. 64 mi. from end of paved road to Ensenada, 7200 ft [2210 m], 6 Jun 1962, J.D.Olmsted 4561 (RSA; somewhat intermediate to Poa secunda). central [region], ca. 3 mi ESE of Prado del Corona, ca. 1 mi up canyon from southernmost aspen colony, tributary of Rio San Rafael, 8100 ft [2490 m], 9 Jun 1962, J.D.Olmsted 4711 (RSA). S of Vallecitos near Cerro la Botella Azul, 30°57'20"N; 115°25'26"W, ca. 2440 m, 27 Jun 1998, J.Rebman 5384 & A. Russell (US). near crest of mountain range, approx. 2 mi SE of the Observatory, 31°14'N, 115°64'W, ca. 2985 m, 28 Jun 1998, J.Rebman 5384 & A.Russell (SD); “Corral Meadow", 7.5 km NW (340°) of the Observatory, 31°06'45"N, 115°29'50"W, 16 Jun 1988, A.C.Sanders 7895, R.Minnich, E.Franco, M.Salazar (RSA, SD, TAES). Vallecitos, ca. 31°02'N, 115°28'W, ca. 2430 m, 18 Jun 1985, R.F.Thorne 60858, R.Dahlgren, S.Boyd & D.Charlton (MEXU, RSA, SD); ditto, ca. 31°02'N, 115°27.5'W, ca. 2430 m, 1 Sep 1985, R.F.Thorne 61394, M.Z.Thorne, L.Thorne & T.Petrella (RSA). just above Observatory living quarters, ca. 31°02'N, 115°28'W, ca. 2600 m, 7 May 1986, R.F.Thorne 61967, T.S.Elias & P.Rojas (MO-3333160, RSA); near gate to UNAM Observatory, 31°02'N, 115°29'30"W, 2520 m, 29 May 1982, G.Yatskievych 82–190, S.Forbes, M.Gallagher, J.Evans & A.Kelley (SD). 55 mi SE of highway 1 on road towards Villecentos at Arroyo Los Alamillos, 31°0.67'N, 115°32.28'W, 2270 m, 24 Sep 2000, P.M.Peterson 15189 & J.Cayouette (US, not flowering). 62 mi SE of highway 1 towards on road towards Villecentos, 31°1.99'N, 115°20.35'W, 2490 m, 24 Sep 2000, P.M.Peterson 15197 & J.Cayouette (US, not flowering).

The species is endemic to the upper elevations of the Sierra San Pedro Mártir, Baja California but apparently was not collected until 1962. Reported and described as Poa orcuttiana Vasey (= Poa secunda) by Gould and Moran (1981); the five collections they mentioned are all Poa bajaensis. Specimens were sometimes labeled as “Poa interior Rydb." (e.g., at SD and TAES). It is well marked by its sparse open panicles, short flag leaf blades, and dense fascicles of old persisting sheaths from which the blades tend to disarticulate.

Hermaphroditic. Annuals (rarely longer-lived); tufted, tufts sparse, small, bases narrow, green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), without cataphyllous shoots, most shoots flowering. Culms (2–)5–60(–70) cm tall, erect or infrequently geniculate at base, slender, leafy, slightly compressed, smooth (or lightly scabrous above); nodes terete, 2–4, usually 1–2 exerted eventually. Leaf sheaths usually compressed and keeled, smooth or keels scabrous; butt sheaths papery, smooth, glabrous; flag leaf sheaths 2–10 cm long, margins fused 25–50% their length, 4 × longer to slightly shorter than its blade; throats and collars smooth, glabrous; ligules 2–6 mm long, usually decurrent, abaxially smooth or scabrous, apices obtuse to acute; blades of cauline leaves (1–)4–15 cm long blades 1–5(–6.5) mm wide, flat or folded, thin, soft, finely scabrous, broadly prow-tipped; flag leaf blade 1–7(–13) cm long, flag leaf blades 1–4(–8) cm long. Panicles (1–)5–15 cm long, mostly over 8 × longer than wide, erect, contracted, cylindrical, sometimes interrupted, congested to loosely congested; rachis with 2–3(–5) branches per node; primary branches erect or steeply ascending, more or less angled, sparsely to densely scabrous; lateral pedicels mostly less than 1/4 the spikelet in length, moderately scabrous, prickles moderately coarse; longest branches 1–7 cm, with 3–15(–25) spikelets in the distal 1/4–1/2. Spikelets 4–7 mm long, ovate to lanceolate, laterally compressed; not bulbiferous; florets 3–7, hermaphroditic; rachilla internodes terete, up to 1 mm long, smooth, glabrous; glumes narrowly lanceolate to lanceolate, subequal, distinctly keeled, keels and sometimes lateral veins scabrous, acute to acuminate; lower glumes 2.2–3.8 mm long, 1–3-veined; upper glumes 2.5–4.8 mm long, subequaling lowest lemma or slightly exceeding it, 3-viened; calluses dorsally webbed, web distinct, hairs woolly; lemmas 2.6–4.3 mm long, lanceolate, green to light green, sometimes slightly anthocyanic, distinctly keeled, smooth, keels to near the top, marginal veins to 2/3, and sometimes intermediate veins short to long villous, between veins glabrous or softly puberulent, intermediate veins obscure to moderately prominent, upper margins white to hyaline, apices acute, pointed or slightly blunt; paleas keels distally with a few hooks, medially softly puberulent to short villous over the keels, intercostal region usually softly puberulent. Flowers mainly cleistogamous; lodicules 0.45 mm long, lanceolate, with a slight lateral lobe at middle; anthers (1–2–)3, 0.2–1.0 mm long. Caryopses 1.8 mm long, narrowly elliptical in side-view, laterally compressed, light brown, sulcus narrow, hilum 0.3 mm long, elliptical, grain adherent to the palea. 2n = 28, 28+I.

The species is endemic to the southwestern USA (Arizona, California, Colorado, Nevada, New Mexico, Oklahoma, Texas, and Utah) and northern Mexico. In Mexico it occurs in Baja California, Baja California Sur, Chihuahua, Coahuila, Nuevo León, and Sonora.

The species occurs in shady sites among rocks and shrubs, usually in loose soils in springtime-moist desert uplands to open slopes lower Pinus-Quercus forests. This species is associated with the Chihuahuan, Sonoran, and Mojave desert vegetation. It occurs between 420–2200 m, and possibly higher. Flowering January to May.

Mexico. Baja California: El Rancho Viejo, 30 Apr 1889, J.S.Brandegee 24 (US). hills behind Bahia de Los Angeles, 3700 ft [1130 m], 24 Feb 1963, R.S.Cowan 2344 (MEXU). Sierra Juárez, 32°27.5'N, 116°09.25'W, 1300 m, 8 May 1982, R.Moran 30600 (MEXU). Sierra La Libertad, Canyon La Borreguera, 9.5 miles E of Mission San Borja, 28°50'N, 113°40'W, 2400 ft [730 m], 27 Mar 1978, K.Nixon 1130, C.P.Cowan & M.L.Sauls (MEXU, TEX). Arroyo San Pedro near La Bocana, 28°28'N, 113°25'W, 250 m, 11 Mar 1966, R.Moran 12512 (TAES). Baja California Sur: N slope of Cerro Azufre, 27°30'N, 112°36'W, 1650 m, 14 Apr 1973, R.Moran 20509 (MEXU, TAES); ditto, 17 Feb 1973, R.Moran 20173 & J.L.Reveal (TAES). Volcán las Tres Vírgenes, 1150 m, R.Moran 20411 (TAES, TEX, US). Chihuahua: ca. del Rio Chihuahua, 5 Apr 1886, G.G.Pringle (MEXU). Mountains. near Paso del Norte, G.R.Vasey s.n. (US). Canon de Tinaja de Corazon, east flank of Sierra de Mulato on Rio Grande 29°13'N, 103°45'W, 750 m, 13 Mar 1986, M.C.Johnston 12898 (TEX). canyon in north face of Sierra Rica, south of Rancho La Consolacion, 19°12'N, 104°05'W, 1400–2000 m, 3 May 1973, M.C.Johnston 10776 (LL). Coahuila: Saltillo, 9 Apr 1905, E.Palmer 532 (NY, US). ca. 2 km N of Estacion Carneros, E flank of Sierra El Chorreadero, 25°08'00"N, 101°07'20"W, 2150 m, 29 Mar 1973, M.C.Johnston 10498, T.L.Wendt & F.ChiangC. (MEXU, MO, TEX). Rio Grande, Tule Canyon above Upper Madison Falls, 29°44−45'N, 102°23'30"W, 475 m, 10 Apr 1973, M.C.Johnston 10618, T.L.Wendt & F.Chiang-C. (MEXU, TEX). Municipio Ramos Arizpe, Sierra de la Paila, 5 Jan 1966, Cano 15 (TAES). [Sierra de Santa Rosa], Rincón de María, on Hacienda La Babia, ca. 70 rd. mi. NW from Múzquiz, 28°27'30"N, 102°05'W, 1900 m, southwest part of rincón, southsouthwest of “Slump Spring", 27 Apr 1975, T.Wendt 901A & D.Riskind (LL). Sierra del Carmen, Rancho Moreros y Rancho San Isidro, ca 178 km de Múzquiz por la brecha Músquiz-Boquillas del Carmen (carretera 53), 28°47'N, 102°30'W, 1300 m, 27 Mar 1992, M.A. Carranzal 398, J.Noriega & L.García (TEX). Nuevo León: Monterey, 17−26 Feb 1880, E.Palmer 1365 (US). Sierra Madre above Monterey, 3000 ft [misprint for 8000 ft? = 2440 m], 31 Mar 1906, C.G.Pringle 13748 (MO, TEX, US). Sonora: N end of Sierra El Viejo, in the large canyon containing Mina Santa Cruz, 25 miles SW of Caborca, vic. 30°22'N, 112°22'W, 1700 ft [520 m], 7 Mar 1983, A.C.Sanders 3527, M.Dimmitt & G.Montgomery et al. (MEXU). SW of Sonoyta on Mexico Highway 8, 31°50'N, 112°56'W, 420 m, 30 Mar 1988, R.S.Felger 88-151 & A.D.Zimmerman (MEXU). Municipio Yecora, 3.5 km W of Santa Ana road, 4.8 km E of San Nicolas road, on Mexico 16, 28°25'40"N, 109°08'50" W, 720 m, 31 Mar 1997, A.L.Reina-G. 97-466 & T.R.VanDevender (MEXU, TEX). 1.5 km SW of Santa Ana on road to Guadalupe Tayopa, 28°22'54"N, 109°09'30"W, 775 m, 21 Feb 1997, T.R.VanDevender 97-207 & A.L.Reina-G. (MEXU, TEX).

Presumably because of its early spring flowering and dependence on winter and early spring precipitation, this species is infrequently collected in Mexico.Its annual habit and narrow, congested panicles, combined with a web on the callus of the lemma, distinguish it from all other species of Poa. The Cano 15 specimen from Coahuila is unusual because the panicle is open and the branches are naked in the lower half, but otherwise it aligns near Poa bigelovii. It was originally determined as “Poa chapmaniana Scribn.?" (but it has 3 anthers ca. 1 mm long, versus 1 ca. 0.2 mm long), then as Poa annua (by Gould in 1966), but it is quite scabrous on the branches and has a strong web on the callus like Poa bigelovii. Plants from Municipio Ramos Arizpe should be examined more closely as a possible new species.

Gynomonoecious. Perennials; tufted, tufts dense, small, low (mostly 3–8 cm tall), with panicles mostly included among the leaves, pallid green to bluish-grey-green, sub-lustrous; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), without cataphyllous shoots, sterile shoots more numerous than flowering shoots. Culms 4–9 cm tall, erect or ascending, sometimes slightly decumbent or geniculate, leafy, terete, smooth; nodes 0–1, not exerted. Leaves mostly basal; leaf sheaths slightly compressed, smooth, glabrous, lustrous; butt sheaths papery, smooth, glabrous; flag leaf sheaths 1.5–4.5 cm long, margins fused ca. 30% their length, ca. equaling its blade; throats and collars smooth, glabrous; ligules (0.5–)1–2.5 mm long, hyaline, abaxially smooth or scabrous, apex obtuse to acute, entire to dentate, sterile shoot ligules like those of the culm leaves; blades 1–6 cm long, 1.5–3 mm wide (expanded), folded, often with strongly involute margins, moderately thick and firm, abaxially smooth sub-lustrous, veins slightly expressed, margins scabrous, adaxially smooth or moderately to densely scaberulous, apex slender prow-tipped; flag leaf blades 1–6 cm long; sterile shoot blades like those of the culm. Panicles 1.5–2.5(–3) cm long, 0.7–1.1 cm wide, erect, contracted to loosely contracted, mostly included in the foliage, congested to moderately congested, with 10–25 spikelets, proximal internode 0.4–0.7 cm long; rachis with 2–6 branches per node; primary branches sub-erect to ascending, stout, more or less terete, moderately densely stiff scabrous all around; lateral pedicels 1/4–1/2 the spikelet length, smooth or sparsely to moderately scabrous, prickles fine, sometimes sub-ciliolate; longest branches 0.8–1.5 cm, with up to 6 spikelets in the distal 1/2. Spikelets (3–)3.5–6(–5.5) mm long, 2–3 × as long as wide, elliptical in side view, to cunniate at maturity, laterally compressed, not bulbiferous, green, sub-lustrous; florets 2, lower hermaphroditic, upper often pistillate; rachilla internodes terete, 0.2–0.3 mm long, smooth, glabrous; glumes broadly lanceolate, central portion green, margins broadly creamy-white scarious, equal, both exceeding the florets, chartaceous on back, smooth, edges obscurely scaberulous, apex firm, acute, sometimes a bit anthocyanic; both glumes (2.5–)3–6(–5.5) mm long, 3-veined; calluses indistinct, glabrous; lemmas 2.3–2.8 mm long, 3-veined, elliptic to oval, pale green, not lustrous, strongly keeled, keel moderately to densely, and upper 2/3 surfaces lightly scaberulous, intermediate veins absent, margins and apex narrowly and briefly scarious-hyaline, edges moderately to sparsely scaberulous; apex obtuse to acute, sometimes denticulate in the upper margin; palea keels finely scabrous, between veins smooth or lightly scaberulous. Flowers; lodicules 0.5 mm long, narrowly lanceolate, unlobed; anthers 0.5–1.1 mm long, those of the upper flower vestigial or sometimes poorly formed but not much reduced. Caryopses 1.3 mm long, elliptical in side-view, laterally compressed, slightly sulcate, hilum oval about 0.2 mm long, grain adherent to the palea. 2n = unknown.

The species occurs in Bolivia and Peru, and in Mexico it is known from the states of Mexico, Puebla, San Luis Potosí, Tlaxcala, and Veracruz.

This species is found on fairly well drained alpine volcanic slopes between 3800–4550 m. Flowering August to September.

Mexico. San Luis Potosí: Virlet d’Aoust 1434 (US fragm.). Puebla: Ixtaccihuatl, Oct 1905, C.A.Purpus 1633 (US). Ixtaccihuatl S flank, in circ E of the “portal" N of La Amacuilecatl (Los Pies), 4400−4450 m, 19.15426°N, 98.63072°W, 3 Oct 1987, R.J.Soreng 3317 & N.Soreng (US). falda SO de Ixtaccihuatl, 3800 m, 1 May 1952, E.Matuda 26104 (US). Municipio de San Nicoas de los Ranchos La Joya, Volcán Ixtaccihuatl, 7 km a N de al carretara pavimento a Amecameca, 3920–4000 m, 28 Oct 1976, S.D.Koch 76236 (US). north side of Popocatepetl, 11 Sep 1957, J.H.Beaman 1732 (US). Mexico: Tlaloc, near summit, 4100–4140 m, 22 Aug 1958, J.H.Beaman 2329 (US). Nevado de Toluca, 1865–1866, Hann s.n. (P, US fragm. ex P-STEUD). Nevado de Toluca, 13500 ft [4115 m], (19°06'00"N, 99°45'36"W), bottom of the crater, 01 Sep 1892, C.G.Pringle 4222 (MO not seen, US, US, US); ditto, summit, 4545 m., 09 Oct 1986, P.M.Peterson 04655 & C.R.Annable (US); ditto, on south rim of crater, 8 Sep 1957, J.H.Beaman 1692 (US). Laguna de Sol, 13 miles east of Mex. highway 3 on road to Nevado de Toluca., 4000 m., 08 Oct 1986, P.M.Peterson 4646 & C.R.Annable (US). Tlaxcala: Malinche, North rim of the crater, 4400–4450 m, 10 Aug 1958, J.H.Beaman 2240 (US). Veracruz: Summit of Cofre de Perote, 19°29'42"N, 97°08'55"W, 4140 m, 20 Sep 1997, S.J.Darbyshire 4806 & M.Gonzáles-Ledesma (US).

First reported from Mexico by Fournier (1886) as Dissanthelium sclerochloides, Beetle (1987) accepted Dissanthelium mathewsii Ball as the correct name. Soreng (1998) and Refulio-Rodríguez et al. (2012) concluded there were too many intermediates between this and the smaller and shorter spikeleted Dissanthelium calycina (J. Presl) Kunth, and therefore, treated the taxon as a subspecies or variety. Poa calycina var. calycina and var. mathewsii are known from Bolivia and Peru. Historically, the species was treated within Dissanthelium. However, DNA analyses have confirmed that all elements of that genus belong within Poa (Refulio-Rodríguez et al. 2012). All but one species formerly placed in Dissanthelium differ from other Poa by having spikelets with two florets, lemmas 3-nerved (rare in Poa), and glumes that are longer than at least the lowest lemma (a feature that occurs infrequently in other groups of Poa). Poa calycina belongs to Poa sect. Dissanthelium (Trin.) Refulio (see also Poa thomasii below).

Peru, in andibus elevatis supra Lima ad 4500 m, Mar 1904, A. Weberbauer 5118 (lectotype: USM!, designated by Anton and Negritto 1997: 237; isolectotypes: BAA-2510!, US-89685! fragm. ex B).

Pistillate. Perennials; mat forming, mats dense (to 20 cm across), low (mostly 1.5–3 cm tall), green; tillers intravaginal (each subtended by a single elongated, tubular prophyll), without cataphyllous shoots. Culms 1–3.5(–5) cm tall, erect or arching, leafy, terete or weakly compressed, smooth; nodes 0–1, not exerted, deeply buried in basal tuft. Leaves mostly basal; leaf sheaths laterally slightly compressed, indistinctly keeled, basal ones with cross-veins, smooth or with sparse hooks, glabrous; butt sheaths becoming papery to somewhat fibrous, smooth, glabrous; flag leaf sheaths 0.8–2 cm long, margins fused ca. 50–60% their length, 2–3 × longer than its blade; throats and collars smooth or slightly scabrous, glabrous; ligules 0.5–3.2 mm long, decurrent, scarious, milky-white, abaxially smooth or scaberulous, upper margin entire or denticulate, apices obtuse to acute, sterile shoot ligules equaling or shorter than those of the upper culm leaves; blades 1–2.2 cm long, 1–1.5 mm wide (expanded), folded, often with involute margins, slightly thick, soft, abaxially smooth, veins slightly expressed, margins proximally scabrous, distally smooth, adaxially smooth or lightly scaberulous, with two rows of buliform cells, but otherwise level, apices abruptly prow-tipped; flag leaf blades like the others; sterile shoot blades like those of the culm. Panicles 0.8–1.5 cm long, 3–7 mm wide, erect, densely contracted, narrowly elliptic to ovoid, erect, slightly secund, included in the leaves or eventually exerted by up to 3(–4) cm, congested, with 5–20 spikelets, peduncle smooth; rachis with 1–2 branches per node; primary branches erect, appressed, stiff, slightly angled, smooth or distally slightly to moderately scaberulous on the angles; lateral pedicels less than 1/4 their spikelet in length, scabrous angled, hooks moderate in size to sub-ciliate; longest branches 0.3–0.4 cm, with up to 4 spikelets, flowered from near the base. Spikelets 4–4.5 mm long, 1.5–2.5 mm wide; 2–3 × as long as wide, ovate, laterally compressed, not bulbiferous, slightly lustrous, two toned; florets (1–)2, pistillate; rachilla internodes terete, mostly 0.2–0.5 mm long, smooth, glabrous; glumes obovate to sub-flabellate, herbaceous and pale green below, scarious bronzy and sometimes anthocyanic in margins and apex, veins distinct, equal to subequal, distinctly keeled, sometimes a bit asymmetrical, smooth, margins broadly scarious-hyaline, edges entire or dentate, smooth, apices dentate to shortly lacerate; lower glumes 2.9–3.3 mm long, 3-veined; upper glumes 3.2–3.3 mm long, 3-veined; calluses glabrous; lemmas 3.5–4.2(–4.5) mm long, 5-veined, obovate to sub-flabellate, thinly herbaceous and pale green below, strongly keeled, surfaces smooth, glabrous intermediate veins distinct, upper margins broadly bronzy-anthocyanic, apices obtuse, sometimes lacerated or dentate; paleas glabrous, keels smooth, closely spaced, between keels smooth (or with a few hooks), Flowers; lodicules 0.4–0.5 mm long, broadly lanceolate, apex rounded; anthers vestigial, 0.1–0.2 mm long. Caryopses 1.8 mm long, elliptical in side-view, cylindrical in cross-section, sulcus indistinct, hilum 0.4 mm long, oval, grain free from the palea, stigma densely plumose. 2n = unknown.

The species occurs in Bolivia, Peru, and Mexico. In Mexico it is restricted to Volcán Ixtaccihuatl, and possibly to the state of Puebla.

The species occurs as isolated mats in wet meadows and on gentle slopes between 4300−4450 m. The spikelets of this species are strictly pistillate and seed is produced apomicticly. Flowering September to October.

Mexico. Mexico or Puebla: Ixtaccihuatl, Jan 1909, C.A.Purpus 3772 (US-924996). Puebla: Ixtaccihuatl, south side of mountain, ca. ½ km NE of summit of Pies, 4300−4350 m, 16 Sep 1958, J.H.Beaman 2555 (MEXU-58016, MSC, US-2381604, TEX, WIS); ditto, in the circ E of the “portal" N of La Amacuilecatl (Los Pies), 19.1507°N; 98.6294°W, 4400−4450 m, 3 Oct 1987, R.J.Soreng 3315 & N.Soreng (US, Soreng 1990, cpDNA voucher).

In Mexico, the Purpus 3772 collection long passed under the name Poa villaroelii Phil. (Hitchcock 1913, Espejo Serna et al. 2000, Dávila Aranda et al. 2006). However, the first author has studied Poa villaroelii in Chile and the herbarium (including types), and concludes the Mexican specimens are not applicable (Soreng et al. 2003, Soreng and Peterson 2007). Poa chamaeclinos has strictly pistillate spikelets, reproduces apomicticly, and has broad, bronze-colored, scareous-hyaline lemma apices, whereas Poa villaroelii (now treated as Poa acinaciphylla E. Desv.) has perfect flowers (anthers 2.2−2.8 mm long) with narrow, whitish, scareous-hyaline apices, and is a much more robust species. Clayton et al. (2006 onwards; accessed Dec. 2011) mistakenly accepted Poa acinaciphylla in Mexico and South America and Poa chamaeclinos only in South America.

A further taxonomic problem arises when trying to reliably distinguish Poa chamaeclinos from Poa perligulata Pilg., a closely related species of South America that also has pistillate spikelets and reproduces apomicticly. Negritto and Anton (2000) argued that Poa chamaeclinos differs by lacking rhizomes, and by having short ligules [0.3−1 (–3) mm long] that have truncate apices with entire, erose or denticulate margins versus longer ligules [1.5−3 (–6) mm long] with acute apices and entire margins in Poa perligulata. The Mexican plants lack rhizomes and the vegetative branching seems to be entirely intravaginal (in Poa perligulata some vegetative extravaginal branching is always present). The ligules in the Mexican specimens are ca. 3 mm long, albeit with the denticulate margins. The ligule length overlaps between these taxa and the margin character is not considered reliable for separating the species. Soreng (1990) initially accepted the Mexican plants as Poa chamaeclinos. However, Soreng et al. (2003a) decided to treat the Mexican plants as Poa perligulata since the Poa chamaeclinos isolectotype at US seemed to be a plant of drier habitat with shorter ligules, stiffer leaves, and slightly scabrous lemmas that are slightly firmer and scareous near the apex. The lectotype of Poa chamaeclinos at USM, illustrated by Anton and Negritto (1997, Fig. 5) seems to fit the Mexican material, whereas their lectotype for Poa perligulata does not (Negritto and Anton 2000). They also indicate that the distinction between the two taxa is difficult and needs further work (Negritto and Anton 2000). If the lack of rhizomes is a good diagnostic character for Poa chamaeclinos, then the Mexican material should be referred to that taxon. Beaman (accompanying notes with the US specimens) considered naming the Mexican plants as a new species with the epithet “cordylina". Unlike Poa gymnantha, which does not tolerate poorly drained soils, Poa chamaeclinos and Poa perligulata grow in perennially wet or “waterlogged" habitats, often with densely-interwoven vegetation. On Ixtaccihuatl, RJS recalls a large population to have occurred over much of the wet floor of the southeastern glacial circ, forming discrete, low mats to about 20 cm in diameter.

Habitat in Europae and Americae septentrionalis, (lectotype: LINN-87.41!, designated by Soreng 2000: 255).

Hermaphroditic. Perennials; extensively rhizomatous, shoots solitary, green or bluish-grey-green; tillers extravaginal (basally cataphyllous), with lateral and downward tending, cataphyllous shoots. Culms 15–60 cm tall, erect, bases usually geniculate, wiry, leafy, strongly compressed, smooth; nodes strongly compressed, 3–4 nodes usually exerted. Leaf sheaths distinctly compressed, minutely rough; butt sheaths papery, smooth, glabrous; flag leaf sheaths ca. 2–6 cm long, margins fused 10–20% the length, subequal to its blade; throats and collars smooth or slightly scabrous, glabrous; ligules 1–3 mm long, abaxially moderately to densely scabrous, upper margin ciliolate, apices obtuse; blades 1.5–4 mm wide, flat or folded, abaxially smooth, veins slightly expressed, margins scabrous, adaxially lightly scabrous over the veins, apices abruptly prow-tipped; cauline blades subequal; sterile shoot blades like those of the culm. Panicles 2–10 cm long, generally 1/6–1/3 as broad as long, erect, contracted or slightly open, linear, lanceoloid to ovoid, often interrupted, sparse to congested, with 15 to 80 spikelets; rachis with mostly 1–3 branches per node; primary branches erect to ascending, or infrequently spreading, fairly strict, 2–3 angled, angles distinctly scabrous (at least in part); lateral pedicels 1/5–2/3 their spikelet in length, scabrous, prickles moderately coarse; longest branches 0.5–3 cm, with 1–15 spikelets. Spikelets (2.3–)3.5–7 mm long, laterally compressed; not bulbiferous; grayish, often anthocyanic tinged, not lustrous; florets 3–7, hermaphroditic; rachilla internodes terete, mostly less than 1 mm long, smooth to muriculate; glumes lanceolate, subequal, distinctly keeled, keels scabrous; apices acute; lower glumes ca. 2 mm long, 3-veined; upper glumes ca. 2.1 mm long, 3-veined; calluses glabrous or more often webbed; web distinct, hairs short, woolly, sparse; lemmas 2.3–3.5 mm long, lanceolate, distinctly keeled, keels and marginal veins short villous proximally, between veins smooth, glabrous, intermediate veins obscure, margins narrowly scarious-hyaline, edges smooth or with sparsely scaberulous, apices obtuse to acute; paleas densely scabrous over the keels, between keels smooth. Flowers chasmogamous; lodicules ca. 0.6 mm long, lanceolate, with a subequal lateral lobe in the upper 2/3; anthers 1.3–1.8 mm long. Caryopses 1.4–1.5 mm long, elliptical in side-view, subtrigonous to subcylindrical in cross-section, brown, shallowly sulcate, hilum 0.2 mm long, oval, grain adherent to the palea. 2n = 35, 42, 49, 50, 56.

This species is circumboreal in distribution and in North America it occurs in Canada, USA, and Mexico (Coahuila).

This strongly rhizomatous, ruderal species occurs in mesic, cool temperate, semi-shaded to open habitats in seasonally soggy soils, sands to clays, both derived from calcareous and igneous substrates. Once established, this species readily spreads by rhizomes.

Mexico. Coahuila: 51.6 km SE of Saltillo and 13 km SE of Jamé on road to Sierra La Viga, 3240 m, 26 Sep 1990, P.M.Peterson 10045, C.R.Annable & J.Valdes-Reyna (US).

This species has been introduced into the New World for soil stabilization and it is presumed also to be native in northern USA and southern Canada (Beal 1896), but has only recently been collected in Mexico. Poa compressa is presumed to be an introduction in Mexico, although the second author has observed this species in other northern Mexico states but did not obtain vouchers because it was not flowering.

Dioecious (sometimes strictly pistillate). Perennials; tufted, sometimes noticeably sub-rhizomatous to long-rhizomatous, tufts dense to a bit loose, generally of medium girth and height (mostly 10–25 cm tall), pale green to bluish-green; tillers mainly intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), usually some extravaginal (basally cataphyllous), with lateral or downward tending, cataphyllous shoots, sterile shoots more numerous than flowering shoots. Culms 15–70 cm tall, erect or bases decumbent, slender or sometimes stout, blades strongly reduced upward, terete or weakly compressed, smooth or slightly scabrous above; nodes terete, 0–1 exerted. Leaves mostly basal; leaf sheaths terete, smooth or scabrous, glabrous or occasionally retrorsely puberulent; bases of butt sheaths thick papery, smooth, glabrous, sub-lustrous; flag leaf sheaths (6–)10–20 or more cm long, margins fused ca. 33% the length, usually more than (5–)9 × long as its blade; collars smooth or scabrous, glabrous or hispidulous; ligules 0.2–18 mm long, decurrent or not, abaxially smooth or scabrous, upper margin ciliolate or glabrous, apices truncate to acuminate; blades of cauline leaves (0.5–)1–3(–4) mm wide, folded, usually involute on the margins, moderately thick and firm, infrequently moderately thin, abaxially smooth or infrequently scabrous, narrowly prow-tipped; cauline blades steeply reduced in length distally along the culm, flag leaf blades usually absent or very reduced, or some up to 1(–3) cm long; sterile shoot blades usually moderately to densely scabrous or hispidulous on and between the veins, or infrequently nearly smooth and glabrous. Panicles 2–12(–30) cm long, erect, contracted (open in anthesis), narrowly lanceoloid to ovoid, congested (except in flowering), with (15–)25–80 (more than 100) spikelets; rachis with 1–2 branches per node; primary branches erect, fairly stout, terete to weakly angled, smooth or scabrous, prickles not confined to angles; lateral pedicels 1/5–1/4 the spikelet in length, sparsely to fairly densely scabrous, prickles fine to fairly coarse; longest branches 1–8 cm, with 3–15(–25) spikelets. Spikelets (3–)4–8(–12) mm long, to 3 × long as wide, sub-lustrous, broadly lanceolate to ovate, laterally compressed, not sexually dimorphic; not bulbiferous; florets 2–7(–13), pistillate or staminate; rachilla internodes terete, usually 0.8–1.3 mm long, smooth, glabrous, sparsely hispidulous, or sparsely softly puberulent to short villous; glumes lanceolate, distinctly keeled, keel smooth or sparingly scabrous, margins fairly broadly scarious, edges smooth or lightly scabrous; apices obtuse to acute; lower glumes distinctly shorter than the lowest lemma, 1–3-veined; upper glumes lanceolate, slightly shorter than lowest lemma, 3-veined; calluses glabrous; lemmas (3–)4.5–6 mm long, lanceolate, pallid green, commonly anthocyanic distinctly keeled, keels and marginal veins short to long villous or softly puberulent, or glabrous, intermediate veins short villous to softly puberulent or glabrous, between veins softly puberulent or glabrous, smooth or sparsely finely scabrous, intermediate veins obscure to moderately prominent, margins narrowly scarious to hyaline, edges smooth or lightly scabrous, apices acute to obtuse, sometimes retusely notched (to 0.25 mm deep); palea keels coarsely scabrous, medially sometimes softly puberulent or long villous, between keels glabrous or infrequently puberulent. Flowers chasmogamous; lodicules of pistillate plants 0.6–0.85 mm long, broadly lanceolate to ovate, with or without a brief lateral lobe from below the middle (lodicules rudimentary in staminate plants); anthers 2–3.2 mm long, or all vestigial and 0.1–0.2 mm long. Caryopses 2–2.5 mm long, elliptical in side-view, subtrigonous in cross-section, honey-brown, sulcus broad and shallow, hilum 0.25 mm long, round, grain adherent to the palea.

The species is widespread in North America and occurs in southwestern and south central Canada, western USA, and northern Mexico in Baja California, Chihuahua, Coahuila, and Sonora.

This dioecious, weakly rhizomatous species occurs in the mountains on open forested slopes derived from calcareous and igneous substrates. It is sometimes strictly pistillate and apomictic. Flowering principally in the spring.

This species provides good springtime forage where it is abundant and all three subspecies occur in Northern Mexico (Soreng and Van Devender 1989; Soreng et al. 2003a). The sex of specimens is indicated here for purposes of estimating the breeding system (geographical and ecological extent of sexual versus asexual reproduction), along with numbers of individuals of each sex where populations were evaluated. Where only or predominately pistillate plants are found, the species usually reproduces apomicticly by seed. No pollen is required to stimulate seed development in apomictic plants of this species (i.e., they are not pseudogamous). Sexual reproduction predominates where staminate plants are found and relatively numerous. Seed is commonly set in 20% or more of flowers in the apomictic populations and usually less than 10% in pistillate plants in sexual populations. Sex-expression is apparently stable in the species of Poa sect. Madropoa, to which Poa fendleriana belongs. The first author grew samples of the species in a common garden over several years and found that plants did not change sex. Individuals of Poa fendleriana occasionally have a few perfect-flowered spikelets, and a few populations containing these unusual plants have been found in Poa fendleriana subsp. fendleriana in New Mexico and Colorado. Poa fendleriana subsp. albescens is a tetraploid whereas the other two subspecies are principally octoploid (Soreng 2005).

A specimen from 20 mi N of Durango, Oct 7 1955, B.Emery 334A (TEX), has one flowering culm of Poa fendleriana mixed in with vegetative parts of Trachypogon. The flowers are pistillate and the lemmas are glabrous to sparsely pubescent on the keel; so it appears intermediate between Poa fendleriana subsp. albescens and Poa fendleriana subsp. fendleriana. However, the habitat seems wrong (low spots in grassland of mesquite, Opuntia, and short grasses), making us wonder if the origin of the one culm stems from a collection sorting error.

Leaf collars often scabrous or hispidulous near the throat; ligules of middle cauline leaves 0.2–1.5 mm long, not decurrent, abaxially smooth or scabrous, upper margin scabrous or ciliolate or glabrous, apices truncate; sterile shoot blades frequently glabrous adaxially. Spikelet rachilla internodes smooth, glabrous; lemma keels and marginal veins smooth or sparingly scabrous, glabrous or sparsely short villous to softly puberulent; palea keels glabrous, between keels glabrous. Lodicules 0.6–0.7 mm long, broadly lanceolate to ovate, with or without a brief lateral lobe from below the middle. 2n = 28, 28+II.

The subspecies is endemic to southeastern Arizona, southwestern New Mexico, USA, and the northern Sierra Madre Occidental of Mexico (Chihuahua, Sonora).

The subspecies is found in canyons and rocky slopes in forests and is associated with: Cupressus, Juniperus, Pinus arizonica Engelm., Poa discolor D.K. Bailey & Hawksw., Poa engelmannii Carrière, Poa leiophylla Schiede ex Schltdl. & Cham., Poa strobiformis Engelm., Populus tremuloides, Quercus hypoleucoides A. Camus, Quercus rugosa Née, Quercus sideroxyla Bonpl., Abies, Pseudotsuga, and Picea chihuahuana Martínez. The subspecies ranges in elevation from 1380–2850 m, and is primarily restricted to regions with summer monsoons and occasional winter snows. Flowering in spring.

Mexico. Chihuahua: Arroyo del Gato, 1 mi W of Talayotes, 27°55'N, 107°49' W, 17 mi SW of San Juanito, 7626 ft [2325 m], 29 Apr 1985, R.J.Soreng 2615, R.W.Spellenberg & R.Corrales (US, population sample: 4♀ & 3♂). Basasiachic, in deep barranca below ca. 240 m waterfall, ca. 6500 ft [1890 m], 28°1'N, 108°15'W, 27 Apr 1985, R.J.Soreng 2606, R.W.Spellenberg & R.Corrales (US, population sample: 14♀ & 4♂). 10 mi SE of Basasiachic on road to San Juanito, 8 mi SE of junction with Yecora–Tomochic road, ca. 8900 ft [2715 m], 28 Apr 1985, R.J.Soreng 2609a, R.W.Spellenberg & R.Corrales (US, population sample: 25♀, 19♂). Municipio Bocoyana, S of San Ignacio Arareco, S of Creel air strip, [27.7°N, 107.7°W], on steep north facing rocky cliffs, ca. 7400 ft [2255 m], 20 Jul 1972, R.Bye Jr. 2404 (TAES♂); ditto, along Rio Oteros, west of Creel, R.A. Bye 3673 (MEXU, TEX ♀). Miñaca, vic. of, [107.35°N, 28.45°W], 1 Apr 1908, J.N.Rose 11648 (US-454361♀). Creel air strip 3 mi due S of Creel, 27°43'N, 107°45'W, 7800 ft [2380 m], 15 Apr 1984, R.J.Soreng 2309 & Spellenberg (NMC, US, sexual population: ♂ & ♀; 2n = 28; Soreng 1990, cpDNA voucher). 5 km SSW of San Juanito, El Rialito, [107.6°N, 27.9°W], 2400 m, 13 May 1974, W.G.Spaulding s.n., P.S.Martin & P.M.Wiseman (ARIZ ♂ & ♀). Rancho Blanco, 28.2°N, 107.6°W, 19 mi N of San Juanito toward La Junta, ca. 6900 ft [2105 m], 29 Apr 1985, R.J.Soreng 2620, R.W.Spellenberg & R.Corrales (US, population sample: 5♀ with high seed, 0♂). 4 mi N of Rancho Blanco, 24 mi N of San Juanito, ca. 6800 ft [2075 m], 29 Apr 1985, R.J.Soreng 2623, R.W.Spellenberg & R.Corrales (US, population sample: 9♀ with much seed, 0♂). Sierra Las Manzanas, 2 km SW of Tosanachic on road to Agua Caliente, ca. 53 km due W of Ciudad Guerrero, 28.30'N, 108°05W, 6396 ft [1950 m], 13 Apr 1984, R.J.Soreng 2305 & R.W.Spellenberg (NMC, US, population sample: 44♀, 34♂; Soreng 1990, cpDNA voucher). Rio Oteros origin above Arroyo El Ranchito, 27°57.5'N, 107°45'W, 11 road mi SW of San Juanito, 7954 ft [2425 m], 29 Apr 1985, R.J.Soreng 2618, R.W.Spellenberg & R.Corrales (US, population sample: 26♀, 9♂). Tomachic, 6.7 mi E and 5 mi W of Cieneguita, on road to Cuauhtemoc, 30 km SW of Ciudad Guerrero, 28°20'N, 107°43'W, 7400 ft [2255 m], 14 Apr 1984, R.J.Soreng 2307 & R.W.Spellenberg (NMC ♀, US ♀, population all pistillate, apomictic, lemmas all glabrous, 2n = 28). crest of pass between Yepomera and Babicora, [29.2°N, 107.9°W], 8 May 1959, D.S.Correll & I.M.Johnston 21635-a (LL♀, very sparsely pubescent to glabrous, intermediate, US♀). between Yepomera and Babicora, [29.2°N, 107.9°W], 8 May 1959, D.S.Correll & I.M.Johnston 21626 (LL, ♀ sparsely pubescent to glabrous, intermediate, US). 9 mi SE of Yoquivo on Basasiachic–San Juanito road, 28.0311°N, 107.9234°W, ca. 7900 ft [2410 m], 28 Apr 1985, R.J.Soreng 2610, R.W.Spellenberg & R.Corrales (US, population sample: 9♀, 10♂). Tal des Rios Tecorichic [garbled] Tarahumare, 4 Apr 1906, Endlich 1209 (US ex B). Sonora: Cananea, 7–8 Jul 1903, D.Griffiths 4865 (US-691228♀; US-306389♀). ca. 3 mi NW of Cananea, road to microwave station N of Mexico Highway 2, ca. 7000ft [2135 m], 31.036°N, 110.375°W, 19 Mar 1982, R.J.Soreng 1780 & R.W.Spellenberg (NMC, US, population sample: 5♂, 2n = 28; Soreng 1990, cpDNA voucher). Santa Cruz, Parry s.n., [Mexican Boundary Survey ] (GH, ♂ very sparse pubescent, ♀ pubescent to sparse pubescent, intermediates; another label on same GH sheet says Munro 165, G.Thurber Herb.). Sierra del Pinito, [30.5°N, 109.5°W], 2500 m, 9 Apr 1977, J.L.Fernandez 3 (ARIZ♀). Sierra Guacomea, Pozo del Santo Nino, Rancho La Alameda, 31°03'22"N, 110°58'06"W, 1472 m, 5 Apr 2005, A.L.Reina-G. 2005-562, T.R.VanDevender & J.Ruiz-C. (ARIZ, US♂); ditto, Rancho La Arboleda, Arroyo El Volteadero, 31°03'10"N, 110°57'04"W, 1385 m, 2 Apr 2005, T.R.VanDevender 2005-493, A.L.Reina-G. & J.Ruiz-C. (ARIZ, US♀).

This subspecies has glabrous lemmas and short ligules, and is the most common subspecies of Poa fendleriana in Mexico. It is often sexually reproducing with dioecious populations and staminate plants are common, but sometimes apomictic individuals with pistillate spikelets are found. Intermediates have sparsely pubescent lemmas and are almost always pistillate. Distribution maps of the subspecies, distribution of staminate and pistillate plants, and a discussion of the breeding system and fossil record is given in Soreng and Van Devender (1989). Hitchcock (1913) suggested this taxon (Poa albescens) is allied to Poa chilensis Trin. (= Poa holciformis J. Presl) from Argentina and Chile, a member of Poa sect. Dioicopoa E. Desv., but DNA data have shown that is not the case (Gillespie et al. 2009).

Leaf collars often scabrous or hispidulous near the throat; ligules of middle cauline leaves 0.2–1.2(–1.5) mm long, not decurrent abaxially scabrous, upper margin usually scabrous or ciliolate, apices truncate to rounded; sterile shoot blades usually scabrous or softly puberulent adaxially. Spikelet rachilla usually smooth and glabrous; lemmas long villous on keels and marginal veins, between veins glabrous or infrequently softly puberulent; palea keels and between keels infrequently puberulent. 2n = 56.

The subspecies is found throughout the range of the species, but is rare to absent from much of the westernmost part of the USA range. In Mexico the subspecies is found in Baja California, Chihuahua, Coahuila, and Sonora.

Where the ranges of the subspecies overlap this subspecies often occurs in slightly drier and more open habitats than Poa subsp. albescens, and more mesic and cooler habitats than Poa. subsp. longiligula. In Mexico this subspecies can tolerate some disturbance as most of the plants are apomictic, except in Coahuila. The subspecies is found in canyons and rocky slopes, from upper arid grasslands (margins) and chaparral of with scrubby species of Quercus, Arbutus, Juniperus, Vaqualina, and Cercocarpus to Hudsonian coniferous forests. Like Poa fendleriana subsp. albescens, this subspecies is primarily restricted to regions with summer monsoons and some winter snows, and ranges from 1900–2200 m. Flowering in spring.

Mexico. Baja California: 4.5 mi S of summit of Cerro 1905, Portezuelo de Jamau, 31°34'N, 115°36'W, 1900 m, 20 Apr 1974, R.Moran 21232 (TAES♀, WYAC♀ intermediate between Poa fendleriana subsp. fendleriana and longiligula, pubescent rachilla, short truncate ligule, probably apomictic). Sierra Juarez, Hansen's Ranch, 21 Jun 1885, C.R.Orcutt 1276a (DS, US♀). Chihuahua: Barranca del Cobre, SE of Creel 28 mi, N of Rio Urique crossing, ca. 7000ft [2135 m], ca. 27.507°N, 107.498°W, 14 Apr 1984, R.J.Soreng 2312 & R.W.Spellenberg (US, population sample: 10♀ 9 subsp. fendleriana; 1 subsp. albescens); ditto, ca. 25 mi SE Creel, ca. 27.534°N, 107.508°W, 2313 (US, population sample: 2♀). N of Basuchil, ca. 10 mi NW of Miñaca, loose crumbling red clay on dry ravine side, near ditch, plateau, arid grassland, 2200 m, 8 May 1929, Y.Mexia 2511 (CAS♀, MO♀). Tomachic, 4.2 mi E on road from La Junta to Yecora, ca. 7000 ft [2135 m], 28.375°N, 107.7865°W, 13 Apr 1984, R.J.Soreng 2306b & R.W.Spellenberg (US, population sample: 24♀ subsp. fendleriana, 2n = 59; 1 subsp. albescens). S of Rancho La Consolacion, canyon in north face of Sierra Rica, 29°12'N, 104°7'W, 1400−2000 m, 3 May 1973, M.C.Johnston, T.L.Wendt & F.Chiang-C. 10776A (LL♀ toward subsp. albescens); ditto, 10773C (LL♀); ditto, 10777 (LL♀). Coahuila: Sierra del Carmen, south peaks of range, NW side of upper Carboneras Canyon, 28°57'N, 102°34'W, 2100 m, 2 Apr 1974, T.Wendt 125, E.Lott & D.Riskind (TEX♂). Municipio de Ocampo, east side of Sierra del Carmen, 28°53'N, 102°28'W, 5200 ft [1590 m], 8 May 1981, D.H.Riskind 2391 (TEX♀).

Discussion. This is the most widespread but least common subspecies of Poa fendleriana in Mexico. Staminate plants are rare or absent, except in Coahuila where a staminate plant has been collected. Poa fendleriana subsp. fendleriana intergrades with Poa fendleriana subsp. albescens in Chihuahua and in southeast Arizona and southwest New Mexico.

Leaf collars smooth to scabrous near the throat; ligules of middle cauline leaves (1.5–)1.8–18 mm long, decurrent, abaxially smooth or lightly scabrous, upper margin usually smooth, glabrous, apices obtuse to acuminate; sterile shoot blades usually scabrous or softly puberulent adaxially. Spikelet rachilla internodes usually sparsely hispidulous or sparsely softly puberulent; lemmas long villous on keels and marginal veins and sometimes intermediate veins, between veins glabrous or softly puberulent (sometimes densely so); palea keels and between keels sometimes puberulent. Lodicules 0.85 mm long. 2n = 56.

The subspecies occurs in North America, southwestern Canada, western USA, and in Baja California, Mexico.

Where their ranges overlap Poa fendleriana subsp. longiligula is fairly restricted to elevations below Poa fendleriana subsp. fendleriana but where there is some winter snow. In Mexico this subspecies is strictly pistillate, apomictic, and distributed between 1300–1900 m. Flowering in spring.

Mexico. Baja California: Hansen’s Ranch, 21 Jun 1885, C.R.Orcutt 1276 (DS♀, DS♀, US). 63 mi SE of Ensenada, 2–3 mi upstream of Rincon, 4.5 mi NE of Santa Catarina, canyon, 4300 ft [1310 m] 22 Apr 1962, R.E.Broder 772 (DS♀, US♀). 4 1/2 mi S of Portezuelo de Jamau, N of Cerro 1905, ca. 31°34'N, 115°36'W, 1775 m, 20 Apr 1974, R.Moran 21226 (CAS♀, ARIZ♀, TAES♀, US). Sierra Juarez, El Progresso, ca. 32°17'N, 115°56'W, 1450 m, 24 May 1975, R.Moran 22044 (TAES♀); ditto, N slope just below summit of Cerro Jamau, ca. 31°34'N, 115°35.5'W, 1890 m, 23 May 1976, R.Moran 23257 (TAES♀); ditto, in steep north slope of Cerro Taraizo, southernmost peak of range, ca. 31°21.75'N, 115°31'W, 1550 m, R.Moran 23007 (TAES♀, ARIZ♀, US); ditto, vicinity of Rancho La Mora, 32°01'N, 115°47'W, 12 Apr 1987, C.Brey 192 (TAES♀). Rancho El Topo, 2 May 1981, A.A.Beetle & R.Alcaraz M-6649 (ARIZ♀, WYAC♀). Sierra San Pedro Mártir, Cañon del Diablo, 31°00'N, 115°24'W, 1700 m, 6 May 1978, R.Moran 25626 (TAES♀).

This taxon was accepted as Poa longiligula by Espejo Serna et al. (2000). Some plants in Baja California of this subspecies are intermediate to Poa fendleriana subsp. fendleriana, but in general the longer smoother margined ligules and puberulent rachillas are diagnostic. Where the two taxa occur in the same area Poa fendleriana subsp. longiligula occurs in more xeric habitats, and Poa fendleriana subsp. fendleriana is found in higher elevations.

Peru, 15°50' to 16°00'S, südlich von Sumbay, Eisenbahn Arequipa–Puno, Tola–Heide, 4000 m, Apr 1914, A.Weberbauer 6905 (lectotype: S! designated by Anton and Negritto 1997: 236; isolectotypes: BAA-2555!, MOL!, US-1498091!, US-2947085! specimen & fragm. ex B, USM!).

Poa ovata Tovar, Mem. Mus. Hist. Nat. “Javier Prado" 15: 17, t.3A. 1965. Type: Peru, Cuzco, Prov. Quispicanchis, en el Paso de Hualla-hualla, 4700 m, 29 Jan 1943, C.Vargas 3187 (holotype: US1865932!).

Poa pseudoaequigluma Tovar, Bol. Soc. Peruana Bot. 7: 8. 1874.Type: Peru, Ayacucho, Prov. Lucanas, Pampa Galeras, Reserva Nacional de Vicunas, entre Nazca y Puquio, Valle de Cupitay, 4000 m, 4 Apr 1970, O.Tovar & Franklin 6631 (holotype: USM!; isotypes: CORD!, MO-3812380!, US-2942178!, US-3029235!).

Pistillate. Perennials; tufted, tufts dense, usually narrow, low (4–6 cm tall), pale green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), without cataphyllous shoots, sterile shoots more numerous than flowering shoots. Culms 4–6 (45) cm tall, erect or arching, leaves mostly basal, terete or weakly compressed, smooth; nodes terete, 0–1, not exerted, deeply buried in basal tuft. Leaves mostly basal; leaf sheaths laterally slightly compressed, indistinctly keeled, basal ones with cross-veins, smooth, glabrous; butt sheaths becoming papery to somewhat fibrous, smooth, glabrous; flag leaf sheaths 2–3.5(–10) cm long, margins fused 30–40% their length, ca. 2.5 × longer than its blade; throats and collars smooth or slightly scabrous, glabrous; ligules to 1–0.5(–7) mm long, decurrent, scarious, colorless, abaxially moderately densely scabrous to hirtellous, apex truncate to obtuse, upper margin erose to denticulate, sterile shoot ligules equaling or shorter than those of the upper culm leaves; blades 1.5–3(–12) cm long, 0.6–1.5(–3) mm wide (expanded), folded to involute, slightly thick, slightly firm, margins involute, abaxially smooth, veins not expressed, margins long scabrous for most of the length, adaxially densely scaberulous, with 2 rows of buliform cells, apex slightly prow-tipped; flag leaf blades like the others; sterile shoot blades like those of the culm. Panicles 1.5–1.7(–8) cm long, 2–2.5(–1.2) mm wide, erect, tightly contracted, linear, slightly secund, included in the leaves or slightly exerted, congested, with 7–10 (many) spikelets, peduncle smooth, proximal internode 0.4–0.7 cm long; rachis with 1–2(–3) branches per node; primary branches erect, appressed, stout, slightly angled, smooth or distally slightly to moderately scabrous to hirtellous on the angles; lateral pedicels less than 1/2 their spikelet in length, moderately scabrous, prickles fine; longest branches 0.3–0.8 cm (?), with 1 to 2 spikelets (?), flowered from near the base. Spikelets 3 mm 6.5 long, 1–1.3(–2.5) mm wide; 2–3 × as long as wide, lanceolate to ovate, laterally compressed, not bulbiferous, slightly lustrous, two toned; florets 1–2(–3), pistillate; rachilla internodes terete, mostly 0.2–0.4 (?) mm long, smooth or scabrous, glabrous; glumes broadly lanceolate, herbaceous and pale green below, scarious bronzy and sometimes anthocyanic in margins and apex, veins distinct, equal to subequal, distinctly keeled, sometimes a bit asymmetrical, subequal to the spikelet, smooth (or scabrous), margins broadly scarious-hyaline, edges entire or dentate, smooth, apices entire; lower glumes 2.5–3(–3.4) mm long, (1–)3-veined; upper glumes 2.7–3(–4.8) mm long, 3-veined; calluses glabrous; lemmas 2.5–3(–5) mm long, 5-veined, (ovate) elliptical (lanceolate), chartaceous green below keeled, surfaces glabrous, proximally smooth, keel and sides distally moderately to densely scabrous (prickle hairs sometimes a bit flexuous) to scaberulous, intermediate veins indistinct, upper margins broadly bronzy-anthocyanic, apex entire, obtuse to acute, paleas glabrous, keels distally scabrous. Flowers; lodicules broadly lanceolate, apex acute, with or without a lateral lobe; anthers vestigial, 0.1–0.2(–0.8) mm long. Caryopses 1.7–1.8 mm long, elliptical in side-view, subcylindrical in cross-section, light honey-brown, sulcus indistinct, hilum 0.25 mm long, round, grain free from the palea. 2n = 70.

In South America the species occurs Argentina, Bolivia, Chile, and Peru; and is known only from the state of Mexico.

This species is typically found on well drained slopes, in loam, sandy loam, scree, or rocky crevices, on alpine volcanic slopes between 4000–4200 m. Flowering in August.

Mexico. Mexico: Monte Tlaloc, near summit of mountain, 4100−4140 m, 22 Aug 1958, J.H.Beaman 2342 (US-2381582, TEX, WIS).

This is the first report of this species for Mexico. Poa gymnantha is known from the high Andes (ca. 8–16°S lat.; Negritto et al. 2008) in Argentina (Jujuy and Salta), Chile (Region 1 and Parinacota), Bolivia (La Paz, Oruro, and Potosí), Peru (Ancash, Apurimac, Arequipa, Ayacucho, Cuzco, Huancavelica, Junín, Moquegua, Puno, and Tacna). Negritto et al. (2008) discusses the taxonomy and reproductive biology of this high polyploid, pistillate, apomictic species. Although low growing forms, often treated as Poa ovata and Poa pseudoaequigluma (see synonyms above)are excluded from Poa gymnantha sensu Negritto et al. (2008), we have made over 84 collections of this species from across its Andean range, and examined many other collections at LPB, US, USM. We cannot find a single morphological feature that can be used to separate these taxa, and instead only see a range or continuum of these features across the entire range. Negritto in Giussani et al. (2012) now accepts Poa ovata and Poa pseudoaequigluma as synonyms with expressed need for further study. The description provided here is based on one small Mexican collection, with extreme ranges from South American material noted in parentheses [given as “(?)" where the full character state range was not documented for South America samples]. In South America small and large plants (Poa gymnantha s.s.) are often mixed within populations, and the stature appears to depend on elevation and microhabitat variations in moisture and light intensity, and exposure to herbivory. Although the type and few other specimens of Poa ovata have well developed stamens, hundreds of other specimens examined have only staminodes and regularly produce seed, a situation that indicates apomixis (Soreng and Van Devender 1989; Negritto et al. 2008). John Beaman (notes in US herbarium) intended to describe his no. 2342 as a new species, with the epithet “acrophila". The features that join the Mexican collection with Poa gymnantha s.l. are the small stature (5 to 6 cm tall); very narrow, contracted panicles (most like the type of Poa pseudoaequigluma); basal sheaths that become a bit fibrous in age; leaf-blades involute, abaxially smooth, with scabrous margins and densely scaberulous adaxial surfaces; ligules abaxially scabrous; lemmas that are glabrous, the apical 1/3−1/4 portion brown, scareous, and scaberulous; and florets pistillate. In contrast to Poa chamaeclinos, the tufts of Poa gymnantha are erect, not mat forming, leaf blades are erect to ascending, involute and adaxially densely scaberulous, the lemmas are distally scabrous with indistinct lateral veins. Although both species generally occur between 4000–5000 m, from our experience in the Andes, Poa gymnantha grows on dry slopes and plains, instead of perennially wet or “waterlogged" habitats. We provide a photo of the Beaman collection from Mexico (Fig. 9) but chose to illustrate a Peruvian specimen with 2-flowered spikelets (Fig. 6 A–E) because the Beaman specimens are quite depauperate and immature. In South America depauperate specimens of the species with one-flowered spikelets are fairly common.

Gynomonoecious or hermaphroditic. Annuals; tufted, tufts mostly small, bases narrow, light green; tillers intravaginal (each subtended by a single 2-keeled, longitudinally split prophyll over 0.5 cm long), without cataphyllous shoots, most shoots flowering. Culms 2–18 cm tall, spreading to erect, sometimes geniculate, slender, leafy, terete, smooth; usually 1 node exerted. Leaf sheaths terete or weakly compressed, smooth, glabrous; butt sheaths thin papery; flag leaf sheaths 1–5 cm long, margins fused ca. 33% their length; throats and collars smooth, glabrous; ligules 0.5–3 mm long, decurrent, abaxially smooth, glabrous, apices obtuse to truncate; blades 1–7 cm long, 1–3(–4) mm wide, flat or weakly folded, thin, soft. smooth, margins usually slightly scabrous, broadly prow-tipped; blades all about equal in length, flag leaf blades well developed. Panicles 1–6 cm long, 1.5–3 × long as wide, erect, more or less open, rhomboid, moderately congested; rachis with 1–2(–5) branches per node; primary branches mostly ascending, straight, terete or sulcate, smooth; lateral pedicels less than 1/5 the spikelet in length, smooth; longest branches 1.5–3 cm, spikelets crowded along the branches, with up to 10 spikelets from the base to distal 1/2. Spikelets 3–5 mm long, lanceolate, laterally compressed; not bulbiferous; florets 2–6, proximal hermaphroditic, distal sometimes pistillate; rachilla internodes terete, smooth, glabrous, usually exposed in side view, distal internode 1/2–3/4 length of distal lemma; glumes unequal, smooth, distinctly keeled, keels smooth, apex acuminate to acute or obtuse, sharp pointed or slightly blunt; lower glumes 1–1.5 mm long, 1-veined, narrowly lanceolate, often slightly sickle shaped, or subulate; upper glumes 2–2.5 mm long, usually shorter than or subequaling lowest lemma, 3-veined, lanceolate to oblanceolate; calluses glabrous; lemmas 2–2.5 mm long, broadly lanceolate, light green, distinctly keeled, smooth throughout, keels, marginal, and intermediate veins densely crisply puberulent to long villous, between veins glabrous, intermediate veins prominent, margins and edges smooth, apices obtuse to acute; paleas keels smooth, short to long villous over the keels. Flowers cleistogamous to weakly chasmogamous; lodicules 0.15–0.2 mm long (the upper sometimes rudimentary); anthers 0.1–0.55 mm long, more or less spherical to short elliptical prior to dehiscence, distal flower ones sometimes vestigial. Caryopses 1.4 mm long, elliptical in side-view, subcylindrical in cross-section, pale green, sulcus almost flat, hilum 0.1 mm long, round to oval, grain slightly adherent to the palea. 2n = 14.

The species is indigenous to western Eurasia, Middle East (especially Mediterranean countries), and North Africa; introduced in Australia and the Americas. In North America the species is known from sporadic locations in British Columbia, Canada; California, Georgia, Oregon in the USA; and Baja California, Mexico. In South America the species is known from Argentina, Bolivia, Chile, Columbia, Peru, and in Central America it has been reported from Guatemala (Soreng et al. 2003b).

This species occurs from near sea level in temperate regions with Mediterranean climates, to elevations with cool temperate to frigid climates in tropical latitudes (to 4400 m). Flowering late winter to early spring.

Mexico. Baja California: between Maneadaro and San Carlos Hot Springs, 18 Apr 1973, A.A.Beetle M-2838 (TAES).

This diploid species name was applied to various early collections from Mexico, and later treated as synonym of Poa annua (Hitchcock 1913, 1935). Poa annua is a tetraploid species derived from Poa infirma × Poa supina (Soreng et al. 2010) that sometimes looks quite similar to its parental types, making identifications challenging. Poa infirma has more crowded and small spikelets on branches that are more ascending, in addition to shorter anthers [0.2−0.5(–0.6) mm], and is a short-lived ephemeral. Soreng et al. (2003a) cited Poa infirma for Mexico, but review of the US vouchers by Hildemar Scholz (B), and subsequently again by RJS and also for MO and MEXU vouchers did not reveal any authentic material. Since then, one authentic specimen was found in a loan from TAES. It is expected to be present elsewhere in Mexico. It is well established in lower elevations of central and southern California west of the Sierra Nevada, and occurs at scattered high elevation locations from Colombia south to Argentina. One old collection from Guatemala, 1880s, H.vonTürckheim 907 (US) originally distributed as Poa infirma, was redetermined by H. Scholz (det. 2007) as Ochlopoa maroccana (Nannf.) H. Scholz (≡Poa maroccana Nannf.). This is the only US specimen from the New World that he determined as this species, and RJS redetermined (det. 2011) it as “Poa infirma?" Only one anther (0.3 mm long) was found on this specimen, pointing to Poa infirma, but the panicles are short and spreading, and more similar in aspect to Poa annua.

Mexico, Durango, Sierra Madre Occidental, southwest slope of Cerro Gordo, just below twin rock outcrops, 23°12'32.5" N, 104°56'54.1"W, 3130−3200 m, 26 Sep 2005, P.M.Peterson & F.Sánchez-Alvarado 19145 (holotype: US!; isotypes: CIIDIR!, MEXU!).

Hermaphroditic. Perennials; tufted, sub-rhizomatous, tufts fairly dense to loose, of moderate girth and height, dark green; tillers mainly extravaginal (basally cataphyllous), with lateral or downward tending, brownish, cataphyllous shoots. Culms 45–80 cm tall, erect or bases slightly decumbent, leafy, terete or weakly compressed, smooth; nodes terete, 2–4, 1–3 exerted. Leaf sheaths compressed, distinctly keeled with a short wing to 0.5 mm deep, smooth, glabrous, or the lower ones sometimes retrorsely scabrous or puberulent; butt sheaths cataphyllous, brownish, smooth, glabrous; flag leaf sheaths 10–15 cm long, margins fused 66–80% the length, 0.4–1.1 × longer than its blade; collars smooth or lightly scabrous, glabrous or ciliate; ligules 3.5–6 mm long, scarious-white to hyaline, abaxially smooth, glabrous, or sometimes puberulent, apex obtuse to acute, entire; blades mostly 10–30 cm long, 2–6 mm wide, flat, to broad-V shaped, thin, lax, abaxial surface and margins lightly scabrous along the veins, adaxially smooth, glabrous throughout, with about 17 veins expressed, apices narrowly prow-tipped; mid-cauline blades 20–30 cm long, ca. 2 × longer than the flag leaf blades, flag leaf blades 12–22 cm long; sterile shoot blades similar to cauline blades. Panicles 12–26 cm long, nodding, open, pyramidal, sparse, with 24–85 spikelets, proximal internode 2.5–5.5 cm long; rachis with (1–)2(–3) branches per node; primary branches ascending to spreading, slender, flexuous, lax, angled, angles sparsely to moderately scabrous; lateral pedicels on average as long as spikelets, moderately scabrous, prickles of moderate coarseness; longest branches 5.5–10 cm, with 3–15 spikelets in the distal 1/3–1/2. Spikelets 4–8 mm long, 1.8–2.7 mm wide, broadly lanceolate, laterally compressed, not bulbiferous, greenish to stramineous; florets 2–3, hermaphroditic; rachilla internodes terete, 1–2 mm long, usually hidden, smooth, glabrous; glumes lanceolate, sub-lustrous, equal to subequal, distinctly keeled, keels scabrous distally, upper surfaces often lightly scabrous, edges smooth or lightly scabrous, apex narrowly acute, lower glumes 3–5 mm long, (1–)3-veined (laterals often short), narrowly lanceolate; upper glumes 3.7–5.6 mm long, distinctly 3-veined, lanceolate to oblanceolate; calluses dorsally webbed, web distinct, hairs 2–3 mm long, woolly; lemmas 4.6–6.3 mm long, lanceolate, 5-veined, green, distinctly keeled, keel and marginal veins glabrous or sometimes proximally sparsely puberulent, distally scabrous, between veins, muriculate to densely scabrous from near the base, intermediate veins distinct, upper margins narrowly scarious-hyaline, edges lightly scabrous, apices acute to narrowly acute, sometimes briefly purple and bronze tinged; paleas 4.4–6 mm long, usually distinctly shorter than the lemma, keels long scabrous for most of the length, between the keels moderately muriculate to short aculeolate. Flowers chasmogamous; lodicules (0.3–)0.6–0.8 mm long, broadly lanceolate to ovate, with a lateral lobe; anthers 2–2.2 mm long, infrequently those of distal flower abortive. Caryopses 2.6–3 mm long, fusiform in side-view, laterally compressed, subtrigonous in cross-section, light brown to olivaceous, sulcus distinct narrow, hilum 0.2–0.25 mm long, oval, grain adherent to the palea. 2n = unknown.

Originally spelled as Poa “matri-occidentalis", the epithet is correctly spelled as matris-occidentalis (fide Kanchi Gandhi). The species is endemic to high mountains on the west side of the central Sierra Madre Occidental in southern Chihuahua to southwestern Durango (Peterson et al. 2006), and is only known from two peaks that are over 300 km apart. Specimens have sometimes passed under the name Poa tracyi Vasey, a species of the mountains of Colorado and New Mexico (Soreng and Hatch 1983, Soreng 1985, 2007). DNA data (Gillespie and Soreng, unpublished, from the holotype) supports the species placement within Poa subgen. Poa supersect. Homalopoa, rather than in Poa sect. Sylvestres as originally postulated in Peterson et al. (2006) based on tenuous morphological connections.

Leaf sheaths smooth, glabrous; collars glabrous; ligules abaxially glabrous. Lemma keel and marginal veins glabrous, between veins muriculate. Lodicules 0.3–0.4 mm long, broadly lanceolate, with a lateral lobe.

This subspecies is known only from Cerro Gordo, Durango.

Known only from a single locality at Cerro Gordo, between 3130–3200 m where the species was found growing on steep, rocky, and grassy slopes beneath open forests of Pseudotsuga menziesii (Mirb.) Franco, Quercus spp., Pinus spp., with other associates, such as: Arctostaphylos pungens Kunth, Bromus carinatus Hook. & Arn., Bromus richardsonii Link, Muhlenbergia cenchroides (Humb. & Bonpl. ex Willd.) P.M. Peterson, Trisetum viride (Kunth) Kunth, Festuca sp., Carex sp., and Agrostis sp. Flowering September and October.

Mexico. Durango: Transect from Paseo de Cerro Gordo to the top (cumbre), 23°12'31.1"N, 104°56'53.0"W, 3136−3348 m, 9 Sep 2006, P.M.Peterson 20011 & F.Sánchez-Alvarado (CIIDIR, US).

Cerro Gordo is quite remote from other high peaks in the area as it takes nearly 10 hours of driving from Durango along a dirt road to reach the base of the mountain, just south of Maiz Gordo. There are other mountains in Durango that approach this height and it would seem reasonable to assume that this species might occur on these.

Mexico, Chihuahua, Municipio de Guadalupe y Calvo, Sierra Madre Occidental, N side of Cerro Mohinora, ca. 13 mi SW of Guadalupe y Calvo, open pine-fir woods with scattered spruce, nearly vertical, N facing rock wall, very moist with many bryophytes and rich herbaceous flora, 25°57'N, 107°03’W, 2950 m, 20 Aug 1988, G.Nesom & A.McDonald 6475 (holotype: TEX!; isotype: ARIZ!).

Leaf sheaths retrorsely scabrous to puberulent; collars ciliate; ligules abaxially puberulent. Lemma keel and marginal veins proximally puberulent, between veins densely scabrous. Lodicules 0.75 mm long, broadly ovate with a broad lateral lobe.

This subspecies is known only from the Sierra Mohinora, Chihuahua.

The subspecies is found on moist rocky ledges and cliffs associated with Juniperus, Pinus, Abies, Picea, Holodiscus, Silene, Cerastium, Deschampsia cespitosa (L.) P. Beauv., Bromus carinatus, Muhlenbergia vaginata Swallen, and Muhlenbergia cenchroides; from 2950–3300 m (see below, Correll’s estimation is too high according to the geodetic mark at the top of the peak). Flowering August to October.

Mexico. Chihuahua: Sierra Mohinora, near Cumbre Mohinora, 25°57'34"N, 107°03'49"W, 3250−3300 m, 13 Sep 2006, P.M.Peterson 20048, F.Sánchez-Alvarado & E.P.Gómez-Ruíz (US); ditto, 20049 (US); ditto, on summit, 10, 000–12, 000 ft [3050−3660 m], 16−17 Oct 1959, D.S.Correll 23177 & H.S.Gentry (LL).

When the second author visited the type locality in 2006, the habitat within 5 km of the peak was found to be quite disturbed by grazing and logging. The holotype was initially determined as Poa tracyi “vel. aff." by J.R & C.G. Reeder in 1989).

Mexico, Nuevo León, Municipio de Galeana, collected in pine woods on the Peak of Cerro Potosí, 21 Jul 1935, C.H. Meuller 2251 (holotype: US-1645320!; isotypes: GH!, US-1646008!).

Hermaphroditic. Perennials; tufted, tufts dense, fairly small and low (mostly 6–10 cm tall), pale green, to slightly bluish-grey-green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), and extravaginal (basally cataphyllous), without lateral or downward tending, cataphyllous shoots, sterile shoots more numerous than flowering shoots. Culms 9–28(–42) cm tall, erect to loosely ascending, sometimes decumbent or geniculate, terete, smooth; nodes 2–3, upper 0–1(–2) exerted, uppermost at mid-culm. Leaves mostly basal; leaf sheaths slightly keeled, smooth, glabrous; butt sheaths papery or becoming slightly fibrous in age, smooth glabrous; flag leaf sheaths 4–8(–11) cm long, margins fused 13–25% their length, sheath ca. 2–6 × longer than its blade; collars smooth, glabrous; ligules 0.25–0.8 mm long, abaxially minutely scabrous, upper margin irregular, minutely scabrous; apex truncate, sterile shoot ligules like those of the culm leaves; blades to 8(–12) cm long, 1–2 mm wide, involute, margins inrolling, soft, moderately thick, abaxially smooth, papilliate, veins slightly expressed, margins scabrous, adaxially papilliate, slightly scabrous over the costae, apex prow-tipped; culm blades more or less equal in length or the middle ones longest, flag leaf blades 0.9–3.5 cm long; sterile shoot blades like those of the culm blades. Panicles 3.4–8 cm long, erect, open, pyramidal, exerted, fairly sparse, with 20–60 spikelet, peduncles and axis smooth or sparsely scabrous, proximal internode 0.7–2 cm long; rachis with branches (1–)2 per node; primary branches widely spreading to reflexed, slightly flexuous, weakly to distinctly angled, moderately to densely scabrous, hooks mostly on the angles, minutely papilliate; lateral pedicels mostly 1/5–1/2 the spikelet in length, sparsely to moderately coarse scabrous, densely papilliate; longest branches 1.4–3.8 cm, with 3–8 spikelets somewhat clustered, in the distal 1/2 to quarter. Spikelets 4–5 mm long, broadly lanceolate to lanceolate, laterally compressed, not bulbiferous, pale green, slightly anthocyanic; florets (1–)2, hermaphroditic; rachilla internodes to 1 mm long (extension to 1.5 mm), smooth, glabrous; glumes broadly lanceolate to lanceolate, usually somewhat anthocyanic, subequal to equal, slightly shorter than adjacent lemmas, distinctly veined, distinctly keeled, slightly thinner than lemmas, smooth or keel apically slightly scabrous, surfaces obscurely papilliate, apex acute; lower glumes 2.5–3.2 mm long, 3-veined; upper glumes 3–3.5 mm long, 2 × to equal lower glumes in width, (3–)5(–7)-veined; calluses glabrous; lemmas 3–4 mm long, broadly lanceolate, lower one 5–7-veined, upper 5-veined, green with or without anthocyanic flush, distinctly keeled, keel smooth or distally sparsely scabrous, keel and marginal veins glabrous or thinly and loosely puberulent, between veins glabrous or loosely puberulent in lower 1/3, intermediate veins prominent, margins and apex narrowly scarious hyaline, edges smooth, apices acute, incurved; palea keels smooth or sparsely to moderately scabrous, glabrous, between keels glabrous or sparsely puberulent. Flowers chasmogamous; lodicules 0.75 mm long, broadly lanceolate, apex sharp, with a well developed lateral lobe; anthers 1.6–2 mm long, sometimes poorly formed. Caryopses 1.8 mm long, elliptical in side-view, round on back, almost cylindrical in cross-section, pale brown, sulcus very shallow, hilum 0.25 mm long, round to oval to elliptical, grain free from the palea. 2n = unknown.

The species is known only from the Cerro Potosí, Nuevo León.

The species occurs on open or sparsely wooded slopes derived from calcareous rocks on the upper slopes of Cerro Potosí, and is associated with Pinus culminicola Andresen & Beaman, Trisetum spicatum (L.) K. Richt., Senecio sp., and Festuca hephaestophila Nees ex Steud., and Festuca hintoniana E.B. Alexeev; between 3650−3800 m. Flowering July to August.

This narrow endemic is locally uncommon.

Mexico. Nuevo León: Cerro Potosí, ca. 20 mi NE of Galeana, ascent of Sierra Potosi by the north hogback, 26 Jul 1934, C.H.Mueller 1248 & M.T.Mueller (GH, MEXU, TEX); ditto, summit, ca. 3650 m, 1 Jul 1959, J.H.Beaman 2643 (GH, MSC, TEX, US). at NE summit of mountain, ca. 3650 m, 13 Sep 1960, J.H.Beaman 4470 (GH, MSC, TEX, US); ditto, 25 Mar 1962, A.A.Beetle M-475 & P.Rojas-M. (WYAC); ditto, 20°52'23"N, 100°13'48"W, 3650 m, 15 Aug 1998, Ing.M.Castillo-B. 345 & Ing.J.Garza-C. (MEXU & MEXU p.p. “b", p.p. “a" is Poa pratensis subsp. alpigena fide RJS on both sheets); ditto, near summit, 3674 m, 21 Oct 2007, P.M.Peterson 21459, J.M.Saarela, & D.Stančik (US; DNA voucher, unpublished); ditto, just below summit, 26 Jul 1985, S.Ginzbarg 217, A.Whittemore & A.McDonald (TEX). Municipio Galeana, 3800 m, 21 Aug 1969, G.B.Hinton 17253 et al. (TEX); ditto, Cima del Cerro Potosí, 3670 m, 3 Aug 1988, A.Garcia 70 (MEXU). 3660 m, 15 Aug 1989, A.Garcia 163, S.Gonzales & M.Gonzalez (MEXU).

Poa mulleri is an odd species perhaps related to Poa orizabensis, but the characters are quite unusual, and it deserves a subsection of its own. Papillae on long cells of the leaf blade in Poa are known from some species of Poa sect. Secundae subsect. Halophyllae Soreng, and from Poa arida Vasey and a few other species. No other species of the genus are known to have multiple small papillae per cell, a character state that to our knowledge is novel in the tribe Poeae, and possibly in Pooideae but is common in Bambusoideae and Ehrhartoideae (Metcalfe 1960). Upper glumes in Poa are almost invariably 3-viened, and when 3 to 5 veins occur, the 5-veined state is infrequent within a species (e.g., Poa macrantha Vasey). In Poa mulleri, the upper glumes are 5–7-veined and the lower lemmas of each spikelet are 5–7-veined. Preliminary DNA data place it in the large supersect. Homalopoa clade (L. Gillespie and N. Amiri pers. com. 2012), for which the sectional and infrasectional taxonomy remains poorly resolved (Gillespie et al. 2009; Soreng et al. 2009).

Poa mulleri Swallen.

From other infrageneric taxa of Poa, differing by the 5−7-veined upper glumes, and long cells of the leaf blade abaxial epidermis with a central line of 6–9 papillae per cell.

Hermaphroditic. Perennials, short-lived; tufted, tufts fairly dense, usually medium girth and height, bases narrow or moderately wide, green, to bluish-green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), and extravaginal (basally cataphyllous), all erect. Culms 20–110 cm tall, erect, slender to stout, leafy, slightly compressed, smooth or scabrous; nodes terete, (3–)4–6, (1–)2–4 exerted. Leaf sheaths distinctly compressed and keeled, usually densely retrorsely scabrous, rarely lightly scabrous, margins not ciliate; butt sheaths papery in age, smooth, glabrous; flag leaf sheaths 5–22 cm long, margins fused (20–)15–50(–60)% the length, subequal to its blade; ligules 3–12 mm long, abaxially densely scabrous, apices acute to acuminate; blades (1.2–)1.5–6(–10) mm wide, flat, lax, abaxial and abaxial surfaces and margins scabrous along the veins, broadly prow-tipped; flag leaf blades 4–18(–30) cm long. Panicles (6–)12–40 cm long, nodding, lax, eventually open, pyramidal, moderately congested, spikelets numerous, to 200+; rachis with (2–)3–7 branches per node; primary branches eventually spreading, drooping, angled, angles densely scabrous; lateral pedicels mostly 1/4–1/2 the spikelet in length, scabrous; longest branches (3–)5–18(–23) cm, with (5–)8–40(–120) spikelets. Spikelets (3–)4–7(–8) mm long, ovate, laterally compressed; not bulbiferous; florets 3–7, hermaphroditic; rachilla internodes terete, less than 1 mm long, smooth or slightly muriculate, glabrous; glumes distinctly keeled, keels scabrous, apex acuminate; lower glumes 2–3.5 mm long, 1–3-veined; upper glumes 2.5–4.2 mm long, shorter than or subequaling lowest lemma, 3-veined; calluses dorsally webbed, web distinct, hairs woolly; lemmas 2.6–4.2 mm long, narrowly lanceolate, distinctly keeled, scabrous distally, keels to 1/2 and marginal veins to 1/3 short to long villous, intermediate veins and between veins usually sparsely softly puberulent, intermediate veins prominent, apices narrowly acute; paleas scabrous, glabrous over the keels. Flowers mainly cleistogamous; lodicules 0.6 mm long, lanceolate; anthers 0.3–1.0 mm long. Caryopses 2 mm long, elliptical-fusiform in side-view, strongly laterally compressed, light brown, sulcus narrow, shallow, hilum 0.2 mm long, elliptical, grain adherent to the palea. 2n = 14, 28.

The species is known from Arizona, Colorado, New Mexico, and Texas, USA; and Coahuila, Mexico (Madera del Carmen).

The species occurs on slopes in wooded canyons with Pinus, Pseudotsuga, Cupressus, Abies, Ceanothus, Cornus stolonifera Michx., Bromus richardsonii Link, Festuca viridula Vasey, Festuca thurberi Vasey, and Quercus;ranging between 2280–2550 m. Flowering August to September.

The species is rare in Mexico.

Mexico. Coahuila: Madera del Carmen; canyon above Campo El Dos, 28°59'23.6"N, 102°36'43.0"W, 2280−2320 m, 8 Sep 2005, P.M.Peterson 18918 & J.Valdes-Reyna (US; DNA voucher, unpublished). 13.8 mi NE of Los Pilares, 28°57'13.0"N, 102°35'7.3"W, 2335 m, 21 Sep 2007, P.M.Peterson 20979, J.M.Saarela, S.Lara-Contreras & J.Reyna-Alvarez (US). 1.8 mi from Campo Uno, up the road towards the summit, 29°0'14.2"N, 102°36'22.7"W, 2547 m, 23 Sep 2007, P.M.Peterson 21036 J.M.Saarela, S.Lara-Contreras & J.Reyna-Alvarez (US).

This is the first report Poa occidentalis for Mexico, and is a range extension of 460 km to the southeast. This species was previously known to occur from eastern Arizona (White Mountains) to southern Colorado, south through the mountains of New Mexico to the Guadalupe Mountains of Eddy County, Texas (Soreng 1985, 2007). Three new collections were gathered in northern Mexico in 2005 and 2007, in the upper coniferous forest belt of the Madera del Carmen, and these presumably represent a relictual population. The first glume of Poa occidentalis was reported as 1-veined (Soreng ibid.), whereas it is principally 3-veined in the Mexican specimens, but re-examination of New Mexican specimens revealed this character state to vary from 1 to 3 veins. Poa occidentalis can be distinguished from other species Poa in Mexico by the following characters: its tall stature; short-lived perennial nature; long acute to acuminate, abaxially scabrous ligules that are longer than the leaf blades are wide; long and widely open, many spikeleted panicles; and anthers 0.5−1.0 mm long. Vasey (1893) considered his Poa trivialis var. occidentalis published in 1885 to be “without description", and taxonomists have traditionally accepted this. However, in 1885, he provided an adequate diagnosis of his indigenous Poa occidentalis var. occidentalis, from Colorado and New Mexico, by comparing it to the introduced Poa trivialis L., which he described and noted had been established in the United States outside of cultivation (mainly in the eastern USA at low to moderate elevations). The isolectotypes indicate “July 1881", and “Mts. near Las Vegas", or “Mts. west of Las Vegas", but there is no habitat “at Las Vegas" for the species, we presume all the material was collected in the mountains near or west of Las Vegas and to be of the same gathering as the lectotype. Vasey’s collection notebooks at US are not helpful and there is only one listing (no. 566) as Poa trivialis under Arizona and New Mexico 1881 (without other details).

Mexico, Puebla, Mt. Orizaba, bald hill, 13, 000 ft [3940 m], spreading, infrequent, 17−18 Aug 1910, A.S.Hitchcock 6254 (holotype: US-691227!; isotype: ISC-66032!).

Hermaphroditic. Perennials; tufted, tufts usually dense, generally medium small girth and height ([5–]10–20 cm tall), green to bluish-grey-green; tillers all or mainly extravaginal (basally cataphyllous), without lateral or downward tending, cataphyllous shoots, or with very short thin ones, sterile shoots more numerous than flowering shoots. Culms 25–60 cm tall, erect or loosely ascending, leafy, terete or weakly compressed, smooth; nodes 2–3, 1–2 exerted. Leaf sheaths strongly compressed, smooth, glabrous; butt sheaths becoming papery to somewhat fibrous, bases of butt sheaths glabrous; flag leaf sheaths 12–18 cm long, margins fused ca. 35% their length, ca.4 × longer than its blade; throats and collars smooth or slightly scabrous, glabrous; ligules 1.6–2 mm long, not decurrent, scarious, white, abaxially moderately to densely scabrous, upper margin erose to denticulate, asperous, apex truncate to obtuse to acute, sterile shoot ligules to 0.5 mm long, mostly shorter than those of the upper culm; blades 1–15 cm long, 2–4 mm wide, folded, somewhat thick and firm, margins involute, abaxially smooth or distally lightly scabrous, margins densely scabrous, adaxially nearly smooth or distinctly scabrous above costae, apex distinctly prow-tipped; flag leaf blades 1–3.5 cm long; sterile shoot blades like those of the culm. Panicles 7–13 cm long, erect or nodding, open, spreading or drooping, with 50–100 spikelets, peduncle scabrous, axis scabrous, proximal internode 1.5–3.8 cm long;; rachis with 1–2(–3) branches per node; primary branches spreading, slender, flexuous, slightly angled, proximally sparsely to moderately scabrous, distally densely scabrous on the angles lightly between them; lateral pedicels usually 1/4–1/2 the spikelet in length, sparsely to moderately scabrous angled, prickles coarse to moderately coarse, sometimes with papillae about the juncture with the glumes; longest branches 2–7 cm, with 10–25 spikelets crowded in distal 1/2. Spikelets 2.5–4.5 mm long, 2–3 × as long as wide, ovate, strongly laterally compressed, not bulbiferous, strongly anthocyanic; florets (1–)2(–4), hermaphroditic; rachilla internodes terete, mostly 0.4–0.8 mm long, smooth or muriculate, glabrous; glumes lanceolate, broadly lanceolate, or ovate, strongly anthocyanic, subequal, distinctly keeled, proximally smooth to scabrous most of the length, distally scabrous on the keel and lateral veins, margins narrowly scarious-hyaline, edges smooth or sparsely asperous, apex acute ; lower glumes 2.5–3.2 mm long, (1–)3-veined, 2/3–4/5 the lower lemma in length, lanceolate to broadly lanceolate; upper glumes 2.5–4.2 mm long, slightly shorter to slightly longer than the lowest lemma, 3-veined; calluses dorsally webbed, web scant, hairs 0.5–1 mm long, woolly; lemmas 2.7–3.4(–3.8) mm long, 5-veined (lowest sometimes 7-veined), ovate to broadly lanceolate, 2.6–4.2 × longer than wide, body firmly chartaceous, green below, apically anthocyanic, strongly keeled, keel and lateral veins and sparsely to densely scabrous, surfaces distally sparsely to moderately scaberulous, keel usually, and marginal veins sometimes, near the base sparsely puberulent, main lateral veins distinct, margins and apex narrowly white scarious to hyaline, apex entire, obtuse to acute; paleas glabrous, keels scabrous for most of the length. Flowers weakly chasmogamous; lodicules 0.35–0.4 mm long, broadly lanceolate, apex obtuse, blunt, with a broad lateral lobe; anthers 0.8–1.1(–1.25) mm long. Caryopses 1.5 mm long, elliptical in side-view, laterally compressed, light olivaceous-brown, sulcus distinct, hilum 0.2 mm long, oval, grain adherent to the palea. 2n = unknown.

The species occurs in Mexico in the states of Mexico, Puebla, and Veracruz; and Guatemala.

This species occurs in subalpine to low alpine meadows and slopes of volcanoes, between (2700–)3000–4300(–4570) m. Flowering July through September.

The species is endemic on the slopes of two volcanoes in Mexico where it is locally common. The disposition of some specimens from the Departamento of Huehuetenango, Guatemala, requires further study.

Mexico. Mexico: Popocatepetl, 12000 ft [3660 m], 5−6 Aug 1910, A.S.Hitchcock 5988 (US). 9000−10000 ft [2725−3050 m], 5−6 Aug 1910, A.S.Hitchcock 6004 (US). Paso de Cortes, 3680 m, 17 Sep 1958, J.H.Beaman 2564 (MEXU). P.N. Izta-Popo, 8 Jul 1980, A.A.Beetle M-5190 (MEXU). Municipio de Tlalmanalco, region de la cabeza del Ixtaccihuatl, La Cienega, 3600 m, 18 Jul 1982, J.Rzedowski 37857 (MEXU). 17 km by road east of Amecameca highway 115 jct., W of Paso del Cortez, 19.097°N, 98.683°W, 3325 m, 2 Oct 1987, R.J.Soreng 3307 & N.Soreng (US). SW flank of Ixtaccihuatl 1 km N of La Joya Trail Head, 19.1507°N, 98.6525°W, 3965 m, 2 Oct 1987 R.J.Soreng 3312 & N.Soreng (US). Paso del Cortez between Popo and Ixtaccihuatl, 19.0858°N, 98.6471°W, 3660 m, 3 Oct 1987, R.J.Soreng 3314 & N.Soreng (DNA barcode voucher, unpublished, and Soreng 1990 cpDNA voucher). Municipio Ixtaccihuatl, Estacion Experimental de Investigation y Ensenanza de Zoquiapan, 8 km south de Rio Frio, Llano Colecto, 3350 m, 12 Sep 1975, S.D.Koch 75519 (TEX). Puebla: Pico de Orizaba, southwest side of mountain in Cañada, 3770 m, 10 Sep 1958, J.H.Beaman 2511 (MEXU, toward Poa ruprechtii). Sierra Negra, SE of Pico de Orizaba, east side of mountain, sandy gravelly soil in grassy meadow on moderately steep slope above timberline, ca. 4200 m., 10 Sep 1958, J.H.Beaman 2517 (TEX, US, WIS, toward Poa ruprechtii). 23 road km above Tlatlachichua, ca. 6 km NNW of Pico de Orizaba, near head of Rio Quatzalapa, ca. 2 km SW of Cerro Mihas, 19.086°N, 97.288°W, 3660 m, 4 Oct 1987, R.J.Soreng 3325 & N.Soreng (US). Municipio Cholula, 30 km E de Cholula, 3000 m, 30 Jun 1989, P.Dávila 391, P.Tenorio & J.Sanches-Ken (MEXU). Ixtaccihuatl, south side of mountain, ca. 6 km N of Paso de Cortes, ca. 3900 m, 18 Jul 1959, J.H.Beaman 2874 (US). Puebla or Veracruz: Mt. Orizaba, 14-15000 ft [4265−4570 m], 25–26 Feb 1892, J.G.Smith 571 (NY). Rio Frio (Camino de Puebla), Jul 1927, E.Lyonnet 68 (US).Veracruz: prope La Joya, 1836, Schiede s.n. (BAA, HAL, LE, US; basis of Poa schiediana Trin ex Steud., nom. nud.); Cordillera, Orizaba, Jun−Oct 1840, H.Galeotti 5767 bis (LE; basis of Poa glycerioides Rupr., nom. nud.).

We have seen a few specimens from Guatemala that are tentatively placed here but verge on the limits accorded to Poa ruprechtii: Huehuetenango, San Juan Ixcoy, ca. del cruce para Chanchocal, 3200 m, J. Rios 6229, N. Hernandez & M. Veliz (MEXU), Sierra de los Cuchumatanes, at km 311 on Ruta National 9N (between Paquix and Chemal, ca. 3360 m, 2 Aug 1959, J.H.Beaman 3011 (MO, US, US “P. atala" ined.). Also reported from Huehuetenango are J.H.Beaman 3799b (US), and J.Rios s.n., N.Hernandez & M.Veliz (MEXU). Poa orizabensis and Poa ruprechtii are difficult to separate when lemma pubescence is scantly developed in the latter, but as interpreted here the former has broader glumes and more compact spikelets, and the sides of the lemmas are glabrous. Further study is needed.

Mexico. Nuevo León, Sierra Madre [Oriental] above Monterey [ca 25°38'N, 100°38'W], calcareous ledges, 3000 ft [misprint for 8000 ft; 2440 m], 31 Mar 1906, C.G.Pringle 10212 (holotype: US-462254!♂; isotypes; GH!, MEXU-539725!♂, MO-1770420!♀, MSC, NMC!, NY-431382!, WYAC).

Differing from Poa ruprechtii Peyr. by leaf collar margins flared (versus not flared), ligules of upper culm leaves truncate (versus obtuse to acute), flag leaf sheaths fused by an invaginated hyaline membrane for much of the upper fusion length (versus abruptly fused by firmly chartaceous margins), spikelet pedicles elongated and moderately to densely scabrous (versus shorter and usually densely to more coarsely scabrous), distal rachilla internodes usually 1–2 mm long (versus less than 1 mm), lemmas thinly chartaceous, intermediate veins faint to moderately prominent, not extending to near the upper margin, margin and apex fairly broadly scarious-hyaline (versus lemmas chartaceous, intermediate veins prominent, extending nearly to the margin, margin and apex narrowly scarious), anthers 1.6–2.8 (versus 0.7–1.05[–1.25]) mm.

Trioecious (mostly hermaphroditic, but some pistillate or staminate). Perennials; tufted, sometimes sub-rhizomatous to rhizomatous, tufts dense to loose, generally medium girth and height, green or bluish-grey-green; tillers extravaginal (basally cataphyllous), and/or mainly intravaginal (each subtended by a single elongated, 2-keeled longitudinally split prophyll), with lateral or downward tending, cataphyllous shoots, or without them. Culms (26–)50–70 cm tall, erect or bases slightly decumbent, fairly slender, not branching above the base, leafy, terete or weakly compressed, smooth; nodes 3–4, terete or slightly compressed, 1–2 exerted. Leaf sheaths slightly compressed, smooth or sparsely to infrequently densely scabrous, glabrous or rarely retrorsely hirtellous to strigulose; butt sheaths papery, smooth, glabrous; flag leaf sheaths (5–)7–18 cm long, margins fused 34–65% the length, fused by an invaginated hyaline margin for much of that length, 1.1–3.1 × longer than its blade; collar margins of lower and mid culm leaves usually flared, smooth or scabrous, glabrous or more often ciliate; ligules 0.8–3 mm long, scarious to hyaline, adaxially scabrous or puberulent, upper margins often ciliolate, apices truncate and entire below to obtuse and irregularly dentate/lacerate above, sterile shoot ligules like those of the culm leaves; blades 2–30 cm long, (1.5–)2–3 mm wide, flat and slightly lax to involute and moderately firm, abaxially and adaxially smooth or lightly scabrous over the veins, margins scabrous, narrowly prow-tipped; lower mid-cauline blades the longest, 10–30 cm long, shorter upward, flag leaf blades 27–50 (90)% longer than their sheaths, flag leaf blade 2.3–10.8 cm long; sterile shoot blades similar to cauline blades or more involute. Panicles 6.5–20 cm long, erect, open, usually trapezoidal to pyramidal, sparse to moderately congested, with (18–)40–100 spikelets, proximal internode (2–)3–5 cm long; rachis with (1–)2–4(–5) branches per node; primary branches spreading to eventually reflexed, fairly flexuous, terete to weakly angled, sparsely to moderately scabrous; lateral pedicels 1/2 to equaling the spikelets, moderately to densely scabrous, prickles fine to moderately coarse; longest branches 4–10 cm, with 3–34 spikelets in distal 1/2, loosely arranged. Spikelets 3–8 mm long, to 3.5 × long as wide, lanceolate, laterally compressed (sexually dimorphic – staminate spikelets with more florets, up to 7–9); spikelets infrequently bulbiferous; florets (2–)3–6(–9), pistillate, staminate, or hermaphroditic; rachilla internodes terete, distal internodes terete, exceeding 1 mm long, smooth or lightly scabrous, glabrous; glumes narrow lanceolate, distinctly keeled; lower glumes 1.6–3.5 mm long, 1/2–2/3 as long as adjacent lemmas, 1-veined; upper glumes 2.2–4.9 mm long, 3-veined; calluses dorsally webbed, web scant to distinct, hairs 1–2 mm long, woolly; lemmas 2.6–5 mm long, lanceolate, 5-veined, body thinly chartaceous, distinctly keeled, keels to 1/3–2/3 and marginal veins to 1/5–1/3 sparsely short to long villous, intermediate veins smooth or sparsely scabrous, glabrous, between veins smooth, glabrous, intermediate veins obscure to moderately prominent, not extending to near the margin, margins smooth, broadly scarious-hyaline, smooth, apices acute; paleas scabrous, medially rarely softly puberulent over the keels. between keels narrow (0.3–0.4 mm), muriculate, scabrous to sparsely puberulent. Flowers chasmogamous; lodicules 0.5 mm long, lanceolate, with a narrow lateral lobe; anthers 1.6–2.8 mm long, sometimes late aborted, infrequently vestigial throughout individual plants. Caryopses 1.8–2.1 mm long, elliptical in side-view, sulcus broad and shallow, brown, hilum 0.2 mm long, round, grain adherent to the palea. 2n = unknown.

The species is endemic to the Sierra Madre Oriental and is found in Coahuila and Nuevo León, Mexico.

This species is found on rocky calcareous substrates in shaded and open forests associated with Pinus, Quercus, and Abies; between 1750−3760 m. Flowering April through October.

The species is a regional endemic, known from only 15 collections over 1400 km2.

Etymology. The new species is named for Dr. Edward Palmer (1829–1911), an important early collector for the U.S. Department of Agriculture, known particularly for his work in southwestern USA and northern Mexico, who, in 1880, was the first to collect this plant. We selected the Pringle collection as type because it is widely distributed.

Specimen examined. Mexico. Coahuila: mountains 6 mi east of Saltillo, Feb to Oct 1880, E.Palmer 1366 (GH, NY, US-924987⚥). Sierra de Los Lirios, 2800 m, Jul to Aug 1942 [error for 1924?], E.Lyonnet 3691 (MEXU-379081⚥, 379082⚥). 22 km SE of San Antonio de las Alazanas, southeast of Saltillo, 20 Jul 1963, F.W.Gould 10538A & D. Watson (TAES). Rincòn de María, on Hacienda La Babia, ca. 70 road miles northwest from Múzquiz, 1750 m, 27 Apr 1975, T.Wendt 883 & D.Riskind (LL). Cima de Sierra la Viga, ca. 3600 m, 24 Oct 1984, A.McDonald 1172 & Gomez (TAES⚥). ceja y ladera s de Sierra La Viga, 3700 m, 22 Aug 1986, A.McDonald 2104 (TEX, TEX). Las Vigas, Cañón de la Carbonera, Sierra de Arteaga, 2100−2600 m, 5 Jun 1987, J.A.Villarreal & M.A.Carranza s.n. (MEXU-469611). Sierra La Marta, east of Cerro Moro, 3400 m, 22 Jul 1985, S.Ginzbarg 148, A.Whittemore & A.McDonald (MEXU-666069♀). Sierra Coahuilon, ca. 3400−3500 m, 18 Jun 1985, A.McDonald 1485 & M.H.Cervera (MEXU-1072101⚥). SE of San Antonio de las Alazanas, SE of Saltillo, at end of road near Summit of Coahuilon, 25.2203°N, 100.3305°W, 3120 m, 17 Oct 1989, P.M.Peterson 8390, J.Valdes-Reyna, & J.Villarreal (US-3518353⚥). 51.6 km southeast of Saltillo and 13 km southeast of Jame on road to Sierra La Viga, 25.33°N, 100.579°W, 3240 m, 26 Sep 1990, P.M.Peterson 10053, C.R.Annable & J.Valdes-Reyna (US). Sierra Zapalinamé, east of Saltillo, 25.3468°N, 100.9016°W, 2700 m, 2 Sep 2005, P.M.Peterson 18787 & J.Valdes-Reyna (US-3496160 (DNA voucher, unpublished, distributed as “Poa ruprechtii"); ditto, E of Saltillo, “El Penitente", 25.3468°N, 100.9016°W, 3070 m, 2 Sep 2005, P.M.Peterson 18790 & J.Valdes-Reyna (US-3496160); ditto, along trail from El Cuatro to El Penitente, 25.3383°N, 100.8882°W, 2925 m, 28 Sep 2007, P.M.Peterson 21127, J.M.Saarela, & S.G.Gómez-Pérez (US; DNA voucher, unpublished). Nuevo León: Cerro Potosí, east slope, 2135 m, 9 Jul 1963, R.L.McGregor 385, L.J.Harms, A.J.Robinson, R.delRosario, R.Segal (US-2454930⚥).

A provisional key to 11 species of Poa in northern Mexico (excluding Baja California) is provided in Peterson et al. (2006). In that paper we concluded that Poa ruprechtii, as widely applied, was heterogeneous. However, until we could examine the type of Poa ruprechtii (C. Heller 312) we could not be sure of the application of the name. Here we emend the description of Poa ruprechtii Peyr. s.s., and treat the material of northeastern Mexico as a new species. Poa palmeri has long been confused with Poa ruprechtii (Fournier 1886, Hitchcock 1913, Beetle et al. 1999, Espejo Serna et al. 2000, Dávila Aranda et al. 2006). Poa palmeri differs in several leaf, panicle, and spikelet characters, and has longer anthers, and the two species do not overlap in geographic range. There is a note on Palmer’s label at US, “Poa ruprechtii Peyr, so named at Kew, S.W. (RJS−presumably Sereno Watson), but scarcely distinct from Poa flexuosa Muhl." (= Poa autumnalis Muhl. ex Elliott of lowlands from the central and southern Appalachians), and a further note; “related to Poa flexuosa" apparently written by A.S. Hitchcock. Interestingly, this name was also applied to the type of Poa ruprechtii at W (Fig. 16). This presumably stems from Peyritsch’s final statement (p. 8) that his new species is like what is now called Poa cuspidata Nutt. (also of the Appalachians), which has sometimes been confused in herbaria with Poa autumnalis. Peyritsch stated, “Scheint mit Poa brachyphylla Schult. (Poa brevifolia Muhl.) verwant zu sein." The latter two names are synonyms of Poa cuspidata Nutt.

Pringle’s label on the type collection can be read as 3000 ft, but we wonder if this is a printing error as the 3 looks more like an 8 when inspected closely, without the serifs of the 3 that are present in the date and other numbers. Whatever the case is, 3000 ft seems far too low for this species.

The breeding system of Poa palmeri is not clear. We tentatively identify it as trioecious because a few specimens are staminate throughout, a few are pistillate, most are hermaphroditic, but some of the later have late aborted stamens. Possibly sex-expression varies within some individuals between late and early season panicles, as seen in sequential gynomonoecism (Soreng and Keil 2003).

It is most easily differentiated from Poa strictiramea by having smooth foliage, more developed lemma and callus pubescence, and smoother lemma surfaces.

Russia, Prov. Sanct-Petersburg, 5 km australi-occidentum, 26 Jun 1997, N.N. Tzvelev N-257 (conserved type: BM! designated by Soreng and Barrie 1998, 157; isotypes: B!, C!, CAN!, CONC!, H!, K!, KW!, L!, LE!, LIV!, MA!, MO!, MW!, NSW!, P!, PE!, PR!, S!, SI!, TNS!, US-3456252!, W!).

Hermaphroditic. Perennials; tufted or not, rhizomatous, shoots solitary or tufted in part, tufts of narrow to medium girth and low to medium height, sometimes forming a dense turf (as in lawns), green, bluish-green, or bluish-gray-green; tillers extravaginal (basally cataphyllous), or also intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), with lateral and downward tending, cataphyllous shoots. Culms 5–70(–100) cm tall, erect or bases decumbent, leafy, terete or weakly compressed, smooth; nodes terete or weakly compressed, 1–2(–3) nodes exposed, proximal node(s) usually not exerted. Leaf sheaths terete to slightly compressed, glabrous or infrequently sparsely to moderately puberulent; butt sheaths papery, smooth, glabrous; flag leaf sheaths 2–20 cm long, margins fused 25–50% the length, 1.2–5(–6.2) × long as its blade; collars smooth, glabrous or ciliate along the margins; ligules 0.9–2(–3.1) mm long, abaxially smooth or scabrous, upper margin ciliolate or glabrous, apices truncate to rounded, infrequently obtuse; blades of cauline leaves 0.4–4.5 mm wide, flat or folded, to involute on the margins, soft and lax to moderately firm, abaxially smooth, glabrous, adaxially smooth or lightly scabrous, frequently with sparse, slender, erect to appressed, curving, sinuous or strait hairs to 0.2–0.8 mm long, broadly prow-tipped or some narrowly prow-tipped; blades subequal, or middle blades longest, flag leaf blades 1.5–10 cm; sterile shoot blades of extravaginal shoots like those of the culm, of intravaginal shoots, when present, sometimes distinctly narrower (0.4–1 mm wide), flat to involute. Panicles 2–15(–20) cm long, erect or nodding, loosely contacted to open, narrowly ovoid to narrowly or broadly pyramidal, sparse to moderately congested, with (25–)30 to over 100 spikelets; rachis with (1–)2–7(–9) branches per node; primary branches spreading early or late, terete or angled, smooth or sparsely to moderately densely scabrous; lateral pedicels usually 1/5–1/2 the spikelet in length, smooth, or sparsely to moderately densely scabrous, prickles fairly fine; longest branches (1–)2–9 cm, with 4–30(–50) spikelets, spikelets usually fairly crowded in distal 1/2. Spikelets 3.5–6(–7) mm long, to 3.5 × long as wide, lanceolate to ovate, laterally compressed, sometimes bulbiferous; florets 2–5, infrequently bulbous basally and leaf-like distally, hermaphroditic; rachilla internodes terete, mostly less than 1 mm long, smooth, glabrous; glumes narrowly lanceolate to lanceolate, infrequently broadly lanceolate, unequal to subequal, usually distinctly shorter than the adjacent lemmas, distinctly keeled, keels sparsely to densely, usually moderately, scabrous, infrequently smooth, apex acute, to acuminate; lower glumes 1.5–4(–4.5) mm long, 1–3-veined, narrowly lanceolate, occasionally weakly sickle shaped; upper glumes 2–4.5(–5) mm long, distinctly shorter to nearly equaling lowest lemma, 3-veined; calluses dorsally webbed, web well developed, sometimes with secondary tufts under each marginal vein, hairs 2–4 mm long, woolly; lemmas 2–4.3(–6) mm long, lanceolate, green or strongly purple colored, distinctly keeled, keels and marginal veins long villous, intermediate veins glabrous or infrequently short villous to softly puberulent, between veins glabrous, smooth or finely muriculate, smooth or lightly scabrous above, intermediate veins prominent, margins narrowly to broadly hyaline, apices acute; paleas scabrous, medially sometimes softly puberulent over the keels, intercostal region narrow, glabrous, or rarely very sparsely and minutely hispidulous. Flowers chasmogamous; lodicules 0.35–0.5(–0.7) mm long, broadly ovate, with a short lateral lobe about midpoint; anthers 1.2–2 mm long, infrequently aborted late in development and ca. 1 mm long. Caryopses 1.5–2 mm long, elliptical in side-view, slightly laterally compressed, subtrigonous in cross-section, brown, sulcus broad, shallow, hilum 0.2 mm long, round to oval, grain adherent to the palea. 2n = 28–147.

The species is distributed worldwide but absent from tropical countries except in high mountains, or where introduced. In Mexico, the species is known from Baja California, Chihuahua, Coahuila, Distrito Federal, Hidalgo, Mexico, Nuevo León, San Luis Potosí and Veracruz. Poa pratensis subsp. agassizensis and subsp. alpigena are possibly native to Mexico.

The facultatively apomictic, mostly high polyploid species inhabits cool mesic to frigid climates, is often seeded for pastures and lawns, and is easily established outside of cultivation since it tolerates disturbance. In Mexico, it occurs from 10–3650 m. Flowering May to July.

Even though the species is highly plastic and tends to look a bit odd in low latitudes, we made an attempt to sort out the subspecific forms in Mexico. The results were unsatisfactory. We have identified a few specimens that match the typical forms, but we could not confidently place most of the material into subspecies. Poa pratensis is primarily a high polyploid and facultatively apomictic (Clausen 1961). It is a common circumboreal species with numerous strains that are treated as species by some authors and as subspecies by others. In Russia (including the former Soviet States) the decision of whether to recognize the various morphological “forms" as subspecies or as distinct species has changed (Tzvelev 1976, Czerepanov 1995) in favor of species, while in the UK Cope and Gray (2009) in the United Kingdom, and Portal (2005) in France Belgium and Switzerland have gone with subspecies. Stoneberg-Holt (2004) correlated morphology and ploidy-level in samples of Poa pratensis collected mainly across Eastern Europe and in Montana in the USA, and grown in a common garden with and without shade. She concluded that there was a continuum of morphological forms that grade from one extreme to another. Plants with predominantly very-fine, moderately firm (form retaining) intravaginal-leaved shoots, and low polyploidy (2n = 28–42) are referable to subsp. angustifolia; these grade into plants with some intravaginal-leaved shoots that are mostly soft-bladed and mainly of middle-ploidy (2n = 42–56) that are referable to subsp. pratensis; these grade into plants with all or most shoots extravaginal, fairly broad-bladed, of mainly higher ploidy (2n = 58–144) referable to subsp. irrigata. Selections by plant breeders from across the range of these forms are all evidently introduced into North America for pastures, soil stabilization, and lawns. However, the cultivated forms have been selected from forms attractive for lawns and most durable to mowing and trampling, and we are no longer dealing with geographic and ecologically differentiated natural taxa. Poa pratensis subsp. alpigena and subsp. agassizensis are probably native and are primarily mid-range polyploids. Our key to subspecies is presented for heuristic purposes; however, in practice it is difficult to draw a firm line between the taxa.

Tufts sparse, some shoots clustered; pale green or bluish-gray-green; tillers intra- and extravaginal. Culms 20–40(–50) cm tall. Ligules of lower culm and tiller leaves commonly glabrous abaxially; lades of cauline leaves flag leaf blades folded, with involute margins, moderately thick, moderately firm; sterile shoot blades usually less than 10 cm long, 0.8–2 mm wide, all folded with involute margins, sparsely pubescent adaxially. Panicles 4–6(–8) cm long, erect or nodding, or loosely contracted or open, ovoid to narrowly pyramidal; rachis with 2–3(–5) branches per node; primary branches steeply ascending to ascending, smooth or sparsely to moderately densely scabrous; longest 1–2.5(–3) cm, with several spikelets per branch. Spikelets lanceolate, not bulbiferous; glumes unequal, glaucous or not; lower glumes 1(–3)-veined; upper glumes shorter than or nearly subequaling the lowest lemma; lemmas 2–3(–3.5) mm long, finely muriculate, intermediate veins glabrous; paleas scabrous, medially glabrous over the keels, intercostal region glabrous. Anthers frequently sterile. 2n = 41, 42, 43, 56.

This subspecies in North America is known from Canada and USA, and in Mexico from the states of Baja California and Coahuila.

The subspecies inhabits cool temperate prairies, meadows, and open coniferous forests.

Mexico. Baja California: Municipio Ensenada, Paraje El Rayo Ejido, 1000 m, 13 May 1997, A.Miranda 1153 (MEXU). Sierra San Pedro Mártir, La Gurulla, 30°54'N, 115°29'W, 2050 m, 29 Jun 1982, R.Moran 30956 (MEXU, TAES). Coahuila: Sierra de Arteaga, Las Vigas, Canon de la Carbonera, 25°20'N, 100°39'W, 2100 m, 5 Jun 1987, J.A.Villarreal 3800 & M.A.Carranza (TAES). Municipio Arteaga, Ejido La Escondida, 25°23'30"N, 100°33'15"W, J.A.Garcia 49 (MEXU).

This form of Poa pratensis, originally described as a species indigenous to Canada and the United States (Boivin and Löve 1960) and now accepted as Poa pratensis subsp. agassizensis, is probably indigenous, but morphologically is questionably distinct from the Eurasian elements of Poa pratensis subsp. angustifolia, or xeric forms of cultivated Poa pratensis subsp. pratensis (Soreng 2007). As originally described it is a taxon with short, ovoid panicles, with small spikelets, and involute leaves. Such specimens are not uncommon among early herbarium collections across Canada and the USA. It approaches Poa pratensis subsp. angustifolia closely, but that subspecies of Eurasian origin has looser panicles, and is generally a lower polyploid (Stoneberg-Holt 2004). Separation of Poa pratensis subsp. agassizensis from Poa pratensis subsp. pratensis is difficult, and so far there is no molecular or cytological data to support it as a separate taxon. We recognize Poa pratensis subsp. agassizensis as a marginally distinct taxon, and site a few vouchers that best match this form.

Tufts sparse, or all shoots solitary; green (often anthocyanic) tillers mainly extravaginal. Culms 15–70 cm tall. Blades of cauline leaves flag leaf blades usually folded, thin, soft; sterile shoot blades less than 15 cm long, 1–3.6 mm wide, flat or folded, usually sparsely pubescent adaxially. Panicles 3–13(–20) cm long, contracted or narrowly pyramidal, expanding well after emergence from the sheath; rachis with (1–)2–6(–7) branches per node; primary branches steeply ascending to eventually spreading or somewhat reflexed, smooth or lightly scabrous; longest branches 1–6 cm, with 5–15 spikelets. Spikelets 4–6.5 mm long, narrowly lanceolate, not bulbiferous; glumes unequal, glaucous or not; lower glumes 1–3-veined; upper glumes subequaling the lowest lemma; lemmas 2.5–3.5 mm long, smooth or finely muriculate, intermediate veins frequently sparsely to moderately densely short villous; paleas scabrous, medially frequently softly puberulent over the keels, intercostal region glabrous, or rarely sparsely hispidulous. 2n = 28, 32, 35, 42, 43, 48, 50, 52, 53, 56, 60, 62, 63, 64, 67–82, 84, 86, 88, 89, 92, ca. 94, ca. 124, 127.

The subspecies is circumboreal and in North America occurs in Canada, Greenland, USA, and Mexico (Nuevo León).

This subspecies is found in boreal to alpine forests, and it tolerates frigid conditions.

This native subspecies is common across Canada, and uncommon in the Rocky Mountains south of Colorado, and locally uncommon in Mexico.

Mexico. Nuevo León: localizado en Galeana, Cerro el Potosi, 20°52'23"N, 100°13'48"W, 3650 m, 15 Aug 1998, Ing.M.Castillo-B. 345 & Ing.J.Garza-C. (MEXU-1072117 & MEXU 999120, p.p. “a", p.p. “b" is Poa mulleri, on both sheets, fide RJS).

Poa pratensis subsp. alpigena is circumboreal and native to the New World in the arctic, alpine, subalpine, and boreal forests (Soreng 2007). This subspecies is recognizable in plastid DNA data (due to a deletion in trn-TLF) and nrDNA sequences as distinct from other subspecies so far evaluated (Gillespie et al. 2005, 2007). In the lower 48 states of USA, Poa pratensis subsp. alpigena occurs at scattered locations as far south as northern Arizona and New Mexico in alpine and subalpine habitats. This subspecies also occurs in Tierra del Fuego, Chile (see type of Poa oligeria). This is the first report of this subspecies for Mexico, where it is probably best considered an interglacial period relict from glacial expansions. It can be separated from the other subspecies by its loose rhizomatous habit, small spikelets, narrow leaves, and narrow (often only slightly spreading) panicles. In North America, it usually has some scant hairs on the intermediate veins of the lemmas and on the palea keels. Several other specimens, particularly from Orizaba, approach this subspecies (see those under subsp. pratensis annotated as “toward alpigena").