Revision of Poa L. (Poaceae, Pooideae, Poeae, Poinae) in Mexico: new records, re-evaluation of P. ruprechtii, and two new species, P. palmeri and P. wendtii

Abstract A revision and key to the 23 species and eight subspecies of Poa (including Dissanthelium) known to occur in Mexico is provided. All voucher specimens seen are cited for accepted taxa, except Poa annua for which one voucher per state is provided. Taxa not previously known from, or poorly understood in, Mexico are discussed.Poa palmeri sp. nov. is endemic to forested slopes of the Sierra Madre Oriental, and we distinguished it from Poa ruprechtii s.s., a species of central Mexico that is here emended to include Poa sharpii (syn. nov.). Poa wendtii sp. nov. is described from the Sierra Santa Rosa in northern Coahuila. Poa tacanae is placed in synonymy in Poa seleri. Poa gymnantha and Poa occidentalis are newly reported for Mexico, and material historically identified as Poa villaroelii areplaced in Poa chamaeclinos.The genus Dissanthelium is considered to belong within Poa, and the Mexican taxa, Dissanthelium calycina subsp. mathewsii and Dissanthelium californicum, are treated as Poa calycina var. mathewsii and Poa thomasii, respectively. Poa subsect. Papillopoa subsect. nov. is erected for Poa mulleri. Lectotypes are designated for Poa conglomerata and Poa seleri.


Introduction
Accounts of the genus Poa L. in Mexico are mostly the result of new species and summary treatments of all grasses in the country, and most are essentially alfataxonomic in nature. Th ese started with J.F. Ruprecht's list of names of grasses collected in Mexico by H. Galeotti (Galeotti 1842), but eff ectively began with Peyritsch (1859) who named two new species. Hemsley's (1882) account, taken from a draft of Fournier's (1886) treatment published four years later, included six species, one of which, Poa ciliaris L. is equal to Eragrostis ciliaris (L.) R.Br. Beal (1896) accounted for four species and Hitchcock (1913) reported 11 species of which fi ve were new. Swallen (1940Swallen ( , 1950 described three more species of Poa from Mexico (and two from adjacent Guatemala), and Beetle (1977) listed 21 species. Manrique de Skendzic (1999) accounted for 12 species with a key to the genus and descriptions, leaving several formerly widely reported taxa unaccounted for. Treatments of Poa in modern checklists covering Mexico (Espejo Serna et al. 2000;Dávila Aranda et al. 2006) recognized 18 and 16 species, respectively. In broader geographical surveys, Soreng et al. (2003a) and Clayton et al. (2006) accepted 16 species in Mexico. Pohl and Davidse (1994) account for fi ve species reaching the Mexican states treated in the Flora Mesoamericana. Soreng (2001) published one new species and discussed others from Baja California, and Peterson et al. (2006) added another species from the Sierra Madre Occidental. Peterson et al. (2006) provided a provisional key to 11 spp. of Poa in northern Mexico (excluding Baja California). In that paper we concluded that P. ruprechtii sensu auct. was heterogeneous. However, until we could examine the type we could not be sure of the correct application. Here we restrict the historically broad application of P. ruprechtii Peyr., and treat the material of P. ruprechtii sensu auct. of northeastern Mexico as a new species. Th e genus Dissanthelium Trin. has recently been submerged into Poa (Refulio-Rodríguez et al. 2012), and the two Mexican species historically treated in that genus are here included in Poa. While examining specimens from northern Coahuila another new species was detected. Due to new discoveries and changes in identifi cation and synonymy, we currently accept 23 species and eight subspecies of Poa, and provide a key to all the Mexican species. lemmas are usually distinctly keeled (except P. secunda), and commonly are pubescent with hairs on the lemma and/or the callus. Th e lemma apex and margins are variously narrowly to broadly scareous-hyaline. Th e lemmas are typically 5-veined but this varies from 3 (P. calycina) to 9 (P. mulleri). Th e palea surface is thinly herbaceous (unlike Koeleria, in which it is hyaline). Th e 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). Th e 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). Th e 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 fl owers are typically reduced to staminodes. Ovaries are glabrous with 2 styles that are apical, approximate, plumose, and white. Th e caryopsis is fi rm (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. Distribution. Th e 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.
Ecology. Species of Poa occur in cool temperate to frigid regions, cool habitats in warm temperate regions, and in dry to wet habitats.
Discussion. 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). Th e 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 fl owered; gynomonoecious (spikelets with lower fl orets perfect and upper ones pistillate); possibly sequentially gynomonoecious (some plants shifting to producing more pistillate fl owers 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 eff ectively obligate (Soreng and VanDevender 1989;Negritto et al. 2008). In Mexico P. chamaeclinos and P. gymnantha are strictly pistillate apomicts, and P. fendleriana is pistillate and apomictic over much of its range. Poa alpina, P. compressa, P. pratensis, and P. 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 - Upper glumes 3-veined; blades and pedicles without papillae (×50); callus pubescent or glabrous; lemmas glabrous or variously pubescent; longest panicle branches ( Uppermost culm sheaths 0.5−1.5 x longer than its blade; fl ag leaf blade welldeveloped, 4-23 cm long; lemmas glabrous or very sparsely puberulent on the keel and marginal veins near the base, infrequently sparsely puberulent between the veins near the base; longest panicle branches (1-) 7−10 (-15) cm long; plants (20-)  Description. 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 fl owering 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; fl ag 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, fl at, moderately thick, soft, straight, mostly basal, smooth or margins lightly scabrous, broadly prow-tipped; upper culm blades reduced in  (2007) E originally drawn from Eggleston 11824 in Hitchcock (1935). length; fl ag 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 fl ower, 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; fl orets 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, Distribution. Th e 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.
Ecology. Th e species is found in disturbed sites in boreal forests, subalpine to low alpine meadows, and rocky slopes, on calcareous to acidic substrates.
Conservation status. Th e species is common in North America and rare (if extant) in Mexico.

Poa chamaeclinos
Ecology. Th e species occurs as isolated mats in wet meadows and on gentle slopes between 4300−4450 m. Th e spikelets of this species are strictly pistillate and seed is produced apomicticly. Flowering September to October. Discussion. In Mexico, the Purpus 3772 collection long passed under the name Poa villaroelii Phil. (Hitchcock 1913, Espejo Serna et al. 2000). However, the fi rst author has studied P. villaroelii in Chile and the herbarium (including types), and concludes the Mexican specimens are not applicable (Soreng et al. 2003, Soreng andPeterson 2007). Poa chamaeclinos has strictly pistillate spikelets, reproduces apomicticly, and has broad, bronze-colored, scareous-hyaline lemma apices, whereas P. villaroelii (now treated as P. acinaciphylla E. Desv.) has perfect fl owers (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 P. acinaciphylla in Mexico and South America and P. chamaeclinos only in South America.
A further taxonomic problem arises when trying to reliably distinguish Poa chamaeclinos from P. perligulata Pilg., a closely related species of South America that also has pistillate spikelets and reproduces apomicticly. Negritto and Anton (2000) argued that P. chamaeclinos diff ers 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 P. perligulata. Th e Mexican plants lack rhizomes and the vegetative branching seems to be entirely intravaginal (in P. perligulata some vegetative extravaginal branching is always present). Th e ligules in the Mexican specimens are ca. 3 mm long, albeit with the denticulate margins. Th e 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 P. chamaeclinos. However, Soreng et al. (2003a) decided to treat the Mexican plants as P. perligulata since the P. chamaeclinos isolectotype at US seemed to be a plant of drier habitat with shorter ligules, stiff er leaves, and slightly scabrous lemmas that are slightly fi rmer and scareous near the apex. Th e lectotype of P. chamaeclinos at USM, illustrated by Anton and Negritto (1997, Fig. 5) seems to fi t the Mexican material, whereas their lectotype for P. perligulata does not (Negritto and Anton 2000). Th ey also indicate that the distinction between the two taxa is diffi cult and needs further work (Negritto and Anton 2000). If the lack of rhizomes is a good diagnostic character for P. 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 P. gymnantha, which does not tolerate poorly drained soils, P. chamaeclinos and P. 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 fl oor of the southeastern glacial circ, forming discrete, low mats to about 20 cm in diameter. Description. 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; fl ag 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, fl at 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; fl orets 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. Discussion. Th is 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 fl owering. Description. 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 bluishgreen; 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 fl owering 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; fl ag 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 fi rm, infrequently moderately thin, abaxially smooth or infrequently scabrous, narrowly prowtipped; cauline blades steeply reduced in length distally along the culm, fl ag 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 fl owering), 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 confi ned to angles; lateral pedicels 1/5-1/4 the spikelet in length, sparsely to fairly densely scabrous, prickles fi ne 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; fl orets 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. Discussion. Th is 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). Th e 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 fl owers 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 P. fendleriana belongs. Th e fi rst author grew samples of the species in a common garden over several years and found that plants did not change sex. Individuals of P. fendleriana occasionally have a few perfect-fl owered spikelets, and a few populations containing these unusual plants have been found in P. 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).

7.
A specimen from 20 mi N of Durango, Oct 7 1955, B.Emery 334A (TEX), has one fl owering culm of Poa fendleriana mixed in with vegetative parts of Trachypogon. Th e fl owers are pistillate and the lemmas are glabrous to sparsely pubescent on the keel; so it appears intermediate between P. fendleriana subsp. albescens and P. 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. Description. 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.

Key to the subspecies of Poa fendleriana
Distribution. Th e 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.
Ecology. Where the ranges of the subspecies overlap this subspecies often occurs in slightly drier and more open habitats than P. subsp. albescens, and more mesic and cooler habitats than P. subsp. longiligula. In Mexico this subspecies can tolerate some disturbance as most of the plants are apomictic, except in Coahuila. Th e 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 P. 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.
Specimens examined. Mexico. Description. 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 fl owering 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 fi brous, smooth, glabrous; fl ag 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, scari- ous, 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 fi rm, 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; fl ag 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 fi ne; longest branches 0.3-0.8 cm (?), with 1 to 2 spikelets (?), fl owered 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; fl orets 1-2(-3), pistillate; rachilla internodes terete, mostly 0. Ecology. Th is 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. Discussion. Th is is the fi rst 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 P. ovata and P. pseudoaequigluma (see synonyms above) are excluded from P. 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 fi nd 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 P. ovata and P. pseudoaequigluma as synonyms with expressed need for further study. Th e 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 (P. 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 P. 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". Th e features that join the Mexican collection with P. gymnantha s.l. are the small stature (5 to 6 cm tall); very narrow, contracted panicles (most like the type of P. pseudoaequigluma); basal sheaths that become a bit fi brous 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 fl orets pistillate. In contrast to P. chamaeclinos, the tufts of P. 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, P. 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-fl owered spikelets (Fig. 6 A-E ) because the Beaman specimens are quite depauperate and immature. In South America depauperate specimens of the species with one-fl owered spikelets are fairly common. Description. 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 fl owering. 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; fl ag 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, fl at or weakly folded, thin, soft. smooth, margins usually slightly scabrous, broadly prow-tipped; blades all about equal in length, fl ag 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; fl orets 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. Distribution. Th e 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).

Poa palmeri
Distribution. Th e species is endemic to the Sierra Madre Oriental and is found in Coahuila and Nuevo León, Mexico.
Ecology. Th is 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.
Conservation status. Th e species is a regional endemic, known from only 15 collections over 1400 km2.
Etymology. Th e new species is named for Dr. Edward Palmer , 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 fi rst to collect this plant. We selected the Pringle collection as type because it is widely distributed.  Peterson et al. (2006). In that paper we concluded that P. ruprechtii, as widely applied, was heterogeneous. However, until we could examine the type of P. ruprechtii (C. Heller 312) we could not be sure of the application of the name. Here we emend the description of P. ruprechtii Peyr. s.s., and treat the material of northeastern Mexico as a new species. Poa palmeri has long been confused with P. ruprechtii (Fournier 1886, Hitchcock 1913, Beetle et al. 1999, Espejo Serna et al. 2000. Poa palmeri diff ers in several leaf, panicle, and spikelet characters, and has longer anthers, and the two species do not overlap in geographic range. Th ere 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 P. fl exuosa Muhl." (= Poa autumnalis Muhl. ex Elliott of lowlands from the central and southern Appalachians), and a further note; "related to P. fl exuosa" apparently written by A.S. Hitchcock. Interestingly, this name was also applied to the type of Poa ruprechtii at W (Fig. 16). Th is presumably stems from Peyritsch's fi nal 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 P. autumnalis. Peyritsch stated, "Scheint mit Poa brachyphylla Schult. (P. brevifolia Muhl.) verwant zu sein." Th e latter two names are synonyms of P. cuspidata Nutt.

Discussion. A provisional key to 11 species of Poa in northern Mexico (excluding Baja California) is provided in
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. Th e breeding system of P. 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).

Poa pratensis
Ecology. Th e 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.
Discussion. 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 subspecifi c forms in Mexico. Th e results were unsatisfactory. We have identifi ed a few specimens that match the typical forms, but we could not confi dently 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-fi ne, moderately fi rm (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 diff erentiated 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 diffi cult to draw a fi rm line between the taxa. Description. 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 fl ag leaf blades folded, with involute margins, moderately thick, moderately fi rm; 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, fi nely muriculate, intermediate veins glabrous; paleas scabrous, medially glabrous over the keels, intercostal region glabrous. Anthers frequently sterile. 2n = 41, 42, 43, 56. Distribution. Th is subspecies in North America is known from Canada and USA, and in Mexico from the states of Baja California and Coahuila.
Ecology. Th is subspecies is found in boreal to alpine forests, and it tolerates frigid conditions. Conservation status. Th is native subspecies is common across Canada, and uncommon in the Rocky Mountains south of Colorado, and locally uncommon in Mexico.

Discussion.
Poa pratensis subsp. alpigena is circumboreal and native to the New World in the arctic, alpine, subalpine, and boreal forests . Th is 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(Gillespie et al. , 2007. In the lower 48 states of USA, P. pratensis subsp. alpigena occurs at scattered locations as far south as northern Arizona and New Mexico in alpine and subalpine habitats. Th is subspecies also occurs in Tierra del Fuego, Chile (see type of Poa oligeria). Th is is the fi rst 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"). Description. Tufts sparse to dense, some shoots clustered; pale green or bluish-graygreen; tillers intra-and extravaginal. Culms 25-80 cm tall. Ligules of lower culm and tiller leaves commonly glabrous abaxially; blades of cauline leaves fl ag leaf blades folded or involute, with involute margins, moderately thick or thin, moderately thin or soft; sterile shoot blades 10-45 cm long, 0.4-1 mm wide, all involute, like or often distinctly narrower than cauline blades, sparsely pubescent adaxially. Panicles 8-18 cm long, loosely contracted, or open and narrowly pyramidal; rachis with 3-6 branches per node; primary branches ascending to spreading, smooth, or sparsely to densely scabrous; spikelets several to many per branch. Spikelets narrowly lanceolate, not bulbiferous; glumes unequal, infrequently glaucous; lower glumes 1(-3)-veined; upper glumes shorter than or subequaling the lowest lemma; lemmas 2.5-3.5 mm long, fi nely muriculate, intermediate veins glabrous; paleas scabrous, medially glabrous over the keels, intercostal region glabrous. 2n = 28, 46, 48, 49-54, 56, 57, 59-66, 72. Distribution. Th is subspecies is native to Eurasia. It is introduced in North America where it is known from Canada, USA, and in Mexico (San Luis Potosí).
Ecology. Th e subspecies is introduced and sometimes is included in pasture grass seed mixes, it tolerates drought better than other subspecies except perhaps subsp. agassizensis. Discussion. Th is Poa pratensis subspecies is more drought tolerant than the others, except perhaps subsp. agassizensis. It is most easily recognized by its very fi ne, relatively fi rm, involute leaf blades that are adaxially pubescent. Th is subspecies name is often applied to collections of subsp. pratensis. Th e latter often has narrow intravaginal leaves but those are softer and adaxially glabrous. According to Stoneberg-Holt's (2004) results, subsp. angustifolia is lower polyploid, and many of the higher counts reported in the literature for this taxon (at least those above 2n = 56) are possibly referable to subsp. pratensis. Ecology. Th e introduced subspecies is cultivated as a turf grass in mesic, cool temperate regions.
Discussion. Th e subspecies is often cultivated for pastures and lawns and many of the cultivars originate from Eurasian selections, or plants selected from foreign strains established in North America; and cultivated strains are certainly present in Mexico (see type of P. bourgeaei). Of more than 700 chromosome counts RJS has compiled from the literature for this taxon the vast majority are between 2n = 80 and 147. Cultivated forms selected for lawns with soft fl at leaves and loose tufts have generally been referred to P. pratensis subsp. irrigata, which is considered Eurasian in origin. Some authors suggest P. pratensis subsp. latifolia (Weihe ex Mert. & W.D.J.Koch) Schübl. & G.Martens is the same taxon and is the correct name (Portal 2005). At the species rank this subspecies has been called P. humilis Ehrh. ex Hoff m. and P. subcaerulea Sm. Poa pratensis is possibly the World' s most complex species, fascinating in itself, but of which we know both much and too little.
Ecology. Th is introduced subspecies occurs mostly between 900-3500 m, in cool temperate habitats, probably in large part due to seeding for soil stabilization, pastures and lawns. Flowering May to July.

Poa ruprechtii
Discussion. In 2005 the fi rst author viewed the type collection of Poa ruprechtii at W and (regrettably) annotated it as "Poa orizabensis Hitchc.?" At that time there was no notation on this specimens indicating it was the type of P. ruprechtii. Subsequent searches for the type at W by Bruno Wallnöfer, and other curators where C. Heller material from Mexico might exist (IB, K, LE, WU), did not relocate this collection until 2011. Th anks to the attentive eyes of Lia Pignotti (W), the type was rediscovered at W in the P. orizabensis folder. Th e type was originally determined as Poa annua L. Th at epithet and author were then crossed out and replaced by P. fl exuosa Muhl. (Fig. 16; see discussion of P. fl exuosa under Poa palmeri). Heller collected on the north slopes of Volcán Toluca between August 10-14, 1846, near Hacienda Cocustepec above the "small hamlets San Buenaventura and Cacalomacan" (Heller and Rugeley 2007; an English translation of Heller's travel's in Mexico, originally published in German). Th e type locality for Poa sharpii, "El Puerto, 7700 ft" in Veracruz, is somewhere above the city of Orizaba on the southeast side of Volcán Orizaba. Th e species should also be searched for on or about the slopes of Volcán Orizaba in Puebla.
Specimens previously identifi ed as "Poa ruprechtii" from Coahuila and Nuevo León, by Hitchcock (1913) and others, belong to P. palmeri (see discussion under that species). Espejo Serna et al. (2000) and Dávila  accepted P. ruprechtii s.l. and P. sharpii. Beetle (1987) attempted to resolve the disposition of the northern plants by placing them in Poa nervosa (Hook.) Vasey. References to the name and material of P. ruprechtii s.l. were simply left out of the volume of Beetle's treatises on the grasses of Mexico that included Poa (Manrique-Skendzic 1999). Th e description of this species given here is based on the material from Mexico cited above. Th e name Poa venosa Swallen has been applied to this taxon in Guatemala, the type of which is a fairly robust specimen of the species, with lemmas quite hairy between the veins. However, other specimens from Guatemala to which that name has been applied are quite variable and approach P. orizabensis. Poa ruprechtii diff ers from P. orizabensis by having lemmas that are distinctly short villous on the keel and lateral nerves and sometimes puberulent between the nerves, versus lemmas that are glabrous or very sparsely puberulent on the base of keel and sometimes the marginal vein, and glabrous elsewhere. Also the glumes cm long, margins fused 25-32% the length; throats and collars smooth or slightly scabrous, glabrous; ligules 1-4 mm long, sometimes decurrent, sub-hyaline, milky-white, abaxially scabrous, apex obtuse to acute, sterile shoot ligules shorter than those of the upper culm leaves; blades mostly 5-10 cm long, 1-3.5(-4) mm wide, fl at, thin, lax, soon withering, distinctly keeled, surfaces and margins sparsely to densely scabrous, apex slenderly prow-tipped; fl ag leaf blades little reduced; sterile shoot blades like those of the culm. Panicles 3-15 cm long, erect, contracted, sub-cylindrical, usually somewhat interrupted, lobed, congested, with 30 to well over 100 spikelets, peduncle and axis moderately to densely scabrous; rachis with 2-3 branches per node; primary branches erect or slightly spreading, fairly strict, angled, densely scabrous on and between angles; lateral pedicels mostly less than 1/5 the spikelet, < 0.5 mm long, densely scabrous, prickles moderately coarse; longest branches 1-7 cm, with 4-60 spikelets, with spikelets congested from the base up to from the lower 1/3 to the apex. Spikelets 3-4 mm long, lanceolate when closed, lanceolate, laterally strongly compressed, not bulbiferous, not shiny, green or sometimes anthocyanic; fl orets (2-)3-4(-5), hermaphroditic; rachilla internodes terete, mostly 0.3-0.4 mm long, smooth, minutely bumpy, or slightly scabrous, glabrous; glumes narrowly lanceolate to lanceolate with a narrow scarious margins, unequal to subequal, shorter than adjacent lemmas, keels scabrous, lateral veins and surfaces smooth or distinctly scabrous, margins scabrous, apex acuminate, sharply pointed, straight or somewhat sickle shaped; lower glumes 1.4-2.8 mm long, 1-veined; upper glumes 1.8-3 mm long, (1-)3-veined; calluses dorsally webbed, commonly with additional webs below the marginal veins, hairs 1-3 mm long, woolly; lemmas 2.5-3 mm long, 5-veined, broadly lanceolate, strongly keeled, keel nearly smooth or scabrous for the upper 1/2, keel to 1/2 and marginal veins to 1/2 sericious, between veins glabrous, distally smooth or scabrous, intermediate veins faint to distinct, sometimes slightly scabrous, margins narrowly scarious distally, scabrous on the edge, apex acute, pointed; paleas distinctly shorter than the lemma, keels scabrous, between keels smooth or lightly scabrous. Flowers mainly cleistogamous or weakly chasmogamous; lodicules 0.5 mm long, lanceolate with a distinct narrow lateral lobe near the middle; anthers 0.4-0.7 mm long. Caryopses 1.1-1.3 mm long, elliptical in side-view, slightly laterally compressed, honey-colored, sulcus shallow, hilum 0.1 mm long, punctiform grain adherent to the palea, styles short, stigmas sparse. 2n = unknown.
Ecology. In Mexico the species is found in mesic, cool temperate forest openings to low alpine habitats, particularly on volcanic substrates, and frequently associated with some disturbance; ranging from 2400−4450 m. Flowering July through October.
Ecology. Th is annual species responds to winter and spring rains and fog on the Pacifi c Coastal Islands of southern California and Baja California Sur. Flowering Mar through May.
Conservation status. Poa thomasii is listed as Federally Endangered in the United States, and it is rare and possibly extinct in Mexico.
Discussion. From the time Bentham placed the species in Dissanthelium up to until Refulio-Rodríguez placed it in Poa (2012), it was known as Dissanthelium californicum (Hitchcock 1913, Beetle 1987, Espejo Serna et al. 2000, Refulio-Rodríguez 2007. DNA data confi rm that all species of Dissanthelium are nested within Poa, and collectively are not monophyletic (Refulio-Rodríguez et al. 2012). Th is species, which is morphologically and phylogenetically isolated from the core species of Dissanthelium placed in Poa sect. Dissanthelium (Trin.) Refulio, is endemic to the Channel Islands of southern California and Isla Guadalupe, Baja California. In Mexico it was collected on Isla Guadalupe by Dr. Edward Palmer in 1875 (Gould andMoran 1981, Beetle 1987). It was thought to be extinct in the United States until it was rediscovered, after grazing pressures from feral goats and pigs, etc., were reduced or removed, on Santa Catalina Island in California (McCune and Knapp 2008). Morphologically, it approaches P. howellii Vasey & Scribn., a species of the adjacent lowlands in California (and north to British Columbia) that also reaches the Channel Islands.
Distribution. Th e new species is known only from the type collection from the Sierra de Santa Rosa, Coahuila.
Ecology. Th e species occurs on sheltered talus and cliff bases, in forests of Abies coahuilensis I.M. Johnst. at 1750 m. Th e only specimen known has perfect fl owers. Flowering in Apr to May.
Etymology. It is our pleasure to name this new species in honor of Th omas Leighton Wendt (born 1950) who collected this and many other plants (including Poa) in the Chihuahuan Desert region.
Conservation status. Th e species is rare. Discussion. Th e type collection is presumed to be a unicate (T.L.Wendt, pers. comm. 2011). Th e species which appears to be endemic to the Sierra de Santa Rosa, should be considered extremely rare and possibly endangered.

Poa acinaciphylla E. Desv. (syn. Poa villaroelii Phil.)
Discussion. Th is taxon is a narrow endemic of the central Andes of Chile and Argentina (Giussani et al. 2012). Reports from Mexico by Hitchcock to Dávila Aranda, from 1913to 2006, as P. villaroellii, and Clayton et al. (2006 (1978−1987), facilitated by fi eld trips with Richard Spellenberg, and loans through NMC from ASU, CAS, DS, GH, MSC, NY, TAES, TEX, WIS, WYAC. RJS visited K in 1992and 2004, W in 2005, and various other herbaria mentioned (BAA, BAB, SI, SGO, USM). We thank the Missouri Botanical Garden and its staff , particularly Gerrit Davidse and Bob Magill (MO), for Tropicos, and its utilities for taxonomic research, and curators at ISC, MEXU, MO, TAES, TEX for recent loans, and W for permission to reproduce type images and for relocating the type of Poa ruprechtii. Appreciation is extended to Alice R. Tangerini for providing new drawings and those of Poa matris-occidentalis; Ingrid Poly-Lin for photos of US specimens; to Mary Barkworth and Utah State University for permission to reissue drawings of Poa prepared by Sandy Long, and Dissanthelium californicum by Hana Pazdirkova and Linda Ann Vorobik for the Flora of North America; to Madroño for letting us reissue the drawing of Poa bajaensis prepared by Nancy Soreng; and to Liliana Giussani and Yolanda Herrera-Arrieta for reviewing the manuscript.