Plants annual or perennial; synoecious sometimes andromonoecious; sometimes rhizomatous, often cespitose, sometimes mat-forming, rarely stoloniferous. Culms 2–300 cm, erect, geniculate or decumbent, usually herbaceous, sometimes becoming woody. Sheaths open, overlapping below; ligules membranous or hyaline (rarely firm or coriaceous), acuminate to truncate, sometimes minutely ciliolate, sometimes with lateral lobes longer than the central portion; blades narrow, flat, folded, or involute, sometimes arcuate. Inflorescences terminal, sometimes also axillary, open to contracted, raceme-like or spike-like panicles; cleistogamous panicles sometimes present in the axils of the lower cauline leaves, enclosed by a tightly rolled, somewhat indurate sheath; disarticulation usually above the glumes, occasionally below the pedicels. Spikelets mostly perfect with 1 (2–6) florets, sometimes staminate or sterile, occasionally paired or in groups of threes then the central spikelet perfect and the lateral ones staminate or sterile; chasmogamous, rarely cleistogamous; glumes usually (0)1(2–3)-veined, apices entire, erose or toothed, truncate to acuminate, sometimes mucronate or awned from the midvein, occasionally awned from the lateral veins; lower glumes sometimes rudimentary or absent, occasionally bifid; upper glumes shorter than to longer than the florets; calluses poorly developed, glabrous or with a few hairs; lemmas glabrous, scabrous or with short hairs, 3-veined (rarely appearing 5-veined), apices awned from the midvein, mucronate or unawned; awns, if present, straight, flexuous, sinuous or curled, sometimes borne between 2 minute teeth, lateral veins occasionally extended into awns; paleas shorter than or equal to the lemmas, 2-veined, apices; anthers (1–2)3, purple, orange, yellow, olivaceous or whitish; ovary with 2 styles, stigmas plumose. Caryopses elongate, fusiform or elliptic, slightly dorsally compressed, rarely laterally compressed, glabrous; hilum short; pericarp fused.

Chromosome base number is × = (8 or 9) 10 and these are relatively small in size.

The genus is primarily distributed in the Western Hemisphere in North Central and South America. There are also seven species known to occur in south-eastern Asia, six of these are found in China (Wu and Peterson 2006).

The species occur in open habitats in deserts, grasslands, sclerophllous scrubland and margins of forests often in xeric to meso-xeric habitats from near sea level to more than 4000 m.

Named for Gotthilf Heinrich Ernst Muhlenberg (1753–1815), a Lutheran minister and pioneering botanist of Pennsylvania, USA.

Caespitose annuals. Culms 30−80 cm tall, slender, terete, glabrous, often branching from the aereal nodes below, usually with stilt-roots from lower nodes. Leaf sheaths usually shorter than the internodes, furrowed, scabrous; ligules 0.5−0.7 mm long, membranous; auricles 1−2 mm long, ciliate, sometimes cauducous at maturity, the cilia about 1 mm long; blades 8−20 cm long, 3−6 (−8) mm wide, flat, scabrous, apex attenuate. Panicles 5−16 (−20) cm long, 1−2.5 cm wide, contracted, spike-like, interrupted, the branches widely spaced along the rachis; primary branches 1−3 cm long, appressed, ascending or divergent and spreading. Spikelets in dense clusters of 2−4 subtended by 10−15 bristles, the bristles 1−5 mm long; glumes 0.7−1 mm long, ovate, membranous, 1-veined, apex awned, bidentate, the awns 3.5−5 mm long; lemmas (1.2−) 2−2.2 mm long, lanceolate, 3-veined, cartilaginous, scaberulous, awned, the awns 10−16 (−20) mm long, straight; callus short, the hairs 0.2−0.4 mm long; paleas as long as the lemmas, 2-veined, these often extending into mucros 0.1−0.3 mm long; stamens 3, anthers 0.7−1 mm long, purplish. Caryopses 1−1.3 mm long, ellipsoid.

Figure 2. 

A−E Muhlenbergia beyrichiana Kunth A habit B ligule with auricles C glumes D floret E stamens and pistil F−H Muhlenbergia maxima Lægaard & Sánchez Vega F habit G end of panicle branch H floret. A−E drawn from A.S. Hitchcock 20635 (US) F−H drawings from Lægaard & Sánchez Vega (1990) drawn from the holotype collection Sánchez Vega & Ruíz Vigo 3561.

Muhlenbergia beyrichiana is known to occur in Brazil, Ecuador and Peru. Earlier, it was reported in Mexico and Central America but these are probably an error for Muhlenbergia diandra (R.W. Pohl) Columbus, a more recently described species that superficially resembles M. beyrichiana (Espejo Serna et al. 2000; Lægaard and Peterson 2001; Peterson et al. 2001).

This species occurs in xerophilic savannahs with Cactaceae, roadsides and along moist ravines; 150−2000 m (Lægaard and Peterson 2001).

Muhlenbergia beyrichiana is morphologically similar to M. pereilema P.M. Peterson, which does not occur in Peru, but can be separated from the latter in having interrupted panicles with divergent primary branches (versus uninterruped panicles with tightly appressed primary branches in M. pereilema), straight lemma awns (versus flexuous or wavy), wide leaf blades 3−6 (−8) mm (versus 2−3 mm) and ciliate auricles (versus not ciliate) [Lægaard and Peterson 2001].

Muhlenbergia beyrichiana is in a clade with M. pereilema and M. plumiseta and is sister to M. flexuosa Hitchc. in M. subg. Muhlenbergia (Fig. 1B; Peterson et al. 2010b).

Peru. Junín: Huancayo, abajo de Pariahuanca, 2000 m, 5 May 1979, Tovar 7880 (US, USM), Tovar 7901 (USM).

Slender often sprawling, caespitose annuals. Culms (4–) 6–30 cm long, glabrous below the nodes; internodes 0.6–6 cm long, glabrous to pilose. Leaf sheaths mostly 0.5–4.8 cm long, shorter than the internodes, glabrous to sparingly pilose; ligules 0.6–1.5 mm long, glabrous, apex mostly truncate, lacerate, auricles absent; blades 1.5–6 cm long, 0.5–1.5(–1.7) mm wide, flat, scaberulent and pubescent above, mostly smooth beneath. Panicles 2–6 cm long, 0.5–1.2 cm wide, open, loosely-flowered; primary branches 0.2–0.6 mm long, excluding the awns, one per node, racemosely inserted. Fertile spikelets 2.4–3 mm long, in fascicles of two, rarely three per branch, often greenish or purplish, the clusters with one short-pedicelled spikelet (bisexual); pedicels (0.0−) 0.2–0.5 mm long (fertile spikelets) and the other two spikelets (sterile or staminate) longer pedicelled; pedicels about 0.7–1 mm long (sterile or staminate); glumes 1–1.3 mm long, narrowly acuminate, apex prolonged, aristate; lemmas 2.4–3 mm long, 3-awned, the central awns (3–) 5–8 (–12) mm long, lateral awns usually 0.8–1.4 mm long; paleas 2.2–2.8 mm long, puberulent, apex aristate, the awns usually 1–1.2 mm long; anthers 0.5–0.7 mm long, yellowish. Caryopses about 1 mm long, obovoid, light brownish.

Figure 3. 

A, B Muhlenbergia bryophilus (Döll) P. M. Peterson A habit B spikelet C, D Muhlenbergia cenchroides (Humb. & Bonpl. ex Willd.) P. M. Peterson C habit D spikelet. Drawings from Giraldo-Cañas and Peterson (2009)A, B drawn from S.G. Beck 818 (LPB) C, D drawn from S.G. Beck 7464 (LPB).

Muhlenbergia bryophilus is found in South America, occuring in Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador and Peru.

This species occurs on moist slopes, cliffs, barrancas, canyons, roadsides and along or near springs usually in shaded areas associated with Cenchrus clandestinus(Hochst. ex Chiov.) Morrone, Bouteloua simplex Lag., Festuca myruos L., Urochloa, Veronica, Eragrostis, Baccharis, Salvia, Agave and Erodium; 1500–3700 m. Flowering December through May.

Muhlenbergia bryophilus is morphologically similar to M. cenchroides and can be separated from the latter in having anthers 0.5−0.7 mm long, the annual habit with culms (4–) 6–30 cm tall and sessile or inconspicuously pedicelled perfect spikelet associated with one (rarely two) staminate or sterile pedicelled spikelet (Tovar 1993; Giraldo-Cañas and Peterson 2009). The central lemmatal awn length of the sessile or inconspicuously pedicelled spikelet was used by Beetle (1948) to differentiate between these two species but we found this measure to be completely overlapping. Muhlenbergia bryophilus is sister to a single entry of M. uniseta (Peterson 24712) in our new analysis (Fig. 1B). We have only a single marker (ITS) for M. bryophilus, so its alignment may change with additional plastid markers.

Peru. Cusco: Prov. Anta, Mollepata−Takawana, C. Vargas C. 19050 (USM); Prov. Urubamba, SW facing slope of Machu Picchu Mountain, V. Ugent 5324 (USM); Junín: Prov. Huancayo, Abajo de Pariahuanca, O. Tovar 7895, 7904 (USM); Cerro E of Huancayo, O. Tovar 2137 (USM); La Libertad: Prov. Bolivar, W of Longotea, 0.5 km towards San Vicente, 7°2'35.6"S, 77°52'39.8"W, 3202 m, 31 Mar 2008, P.M. Peterson 21966, R.J. Soreng & J. Montoya Quino (US, USM); Lima: Prov. Canta, 8 km SW of San Jose Canta towards Huamantango, 11°31'10"S, 76°42'16.3"W, 2770 m, 28 Mar 2004, P.M. Peterson & N. Refulio Rodríguez 17995 (US, USM); Piura: Prov. Huancabamba, La Beatita, S. Llatas Quiroz 1850, 1851 (CPUN); Puno: Prov. Sandia, Debajo de Cuyocuyo, R. Ferreyra & A. Vera Beuner 16636 (USM).

Peru, Cajamarca, Micuypampa, 62 km from Cajamarca towards Celendín, 3600 m, 26 Mar 1988, S.A. Renvoize & S. Lægaard 4962 (holotype: CPUN!; isotypes: AAU!, K!, MO-3712393!, US-3185350!).

Loosely caespitose perennials. Culms 8−12 cm tall, 0.2−0.4 mm diameter just below the panicle, erect to decumbent near base, slender, scaberulous to glabrous, profusely branched below; lower internodes 5−10 mm long with repeated intravaginal branching. Leaf sheaths 4−27 mm long, glabrous, generally longer than the internodes, rounded near base; ligules (1.5−) 1.8−2.5 mm long, hyaline, often lacerate, margins decurrent, apex obtuse; blades 0.5−1.5 cm long, 0.6−1.2 mm wide, flat or folded, prominently veined, sometimes conspicuously crystalline or spiculate on both surfaces, otherwise glabrous below, sparsely scaberulous above and along margins, tapering to a boat shaped tip. Panicles (1.0−)1.5−4.0 cm long, 1−3 mm wide, exserted or included in the uppermost sheath, loosely contracted, narrow; primary branches 0.5−2 cm long, appressed to the culm axis, one per node.pedicels 1−5 mm long, stiff, densely scabrous, spiculate, erect; nodes 4−6 per inflorescence. Spikelets 2.4−2.8 mm long (excluding the mucro or awn), plumbeous to reddish-purple; glumes 1.2−1.6 mm long, shorter than the floret, subequal to equal, 1-nerved, glabrous, often reddish-purple near apex and greenish-grey below, apex obtuse; lemmas 2.4−2.8 mm long, lanceolate, keeled, prominently 3-nerved, dark reddish-purple to plumbeous above greenish-grey below, sericeous, lower ½ to ¾ with scattered appressed hairs, the hairs 0.3−0.5 mm long, apex acuminate, mucronate or short-awned, the awn up to 1.5 mm long, scabrous; paleas 2.4−2.6 mm long, as long as the lemma, lanceolate, hairy between the nerves; anthers 1−1.3 mm long, purple or yellow. Caryopses 0.9−1.1 mm long, elliptic to fusiform, terete, yellowish-brown.

Figure 4. 

A−C Muhlenbergia caxamarcensis Lægaard & Sánchez Vega A habit B panicle branch C floret D−G Muhlenbergia ciliata (Kunth) Trin D habit E ligule F glumes G floret. Drawings A−C from Lægaard and Sánchez Vega (1990) from holotype collection (S.A. Renvoize & S. Lægaard 4962) D−G from Peterson and Annable (1991) drawn from P.M. Peterson & C.R. Annable 4541 (WS).

This species is endemic to Peru, known only from Cajamarca and La Libertad departments.

Muhlenbergia caxamarcensis occurs on shallow soils on rock shelves and rocky outcrops often of calcareous origins, mud flats, open grassy meadows and slopes associated with Festuca, Carex, Calamagrostis (probably better treated as Cinnagrostis Griseb. but combinations are not yet made; Saarela et al. 2017, Soreng et al. 2017), Polylepis, Muhlenbergia ligularis, M. peruviana and M. cenchroides; 3000−3600 m. Flowering March through May.

Muhlenbergia caxamarcensis is morphologically similar to M. ligularis and M. fastigiata and can be separated from both of these species in possessing sericeous florets (lemma and palea) with hairs readily visible under 10× magnification.

Muhlenbergia caxamarcensis is a member of M. subg. Bealia and is sister to the North American M. filiformis (Thurb. ex S. Watson) Rydb.– M. vaginata Swallen pair (Peterson et al. 2010b). In our new analysis, M. caxamarcensis appears to have evolved within M. ligularis (Fig. 1A, plastid only). However, the ITS marker clearly aligns M. caxamarcensis with a single accession of M. ligularis (Fig. 1A). This pair is sister to M. filiformis and all three accessions are sister to M. vaginata. These results suggest multiple origins for M. caxamarcensis from North and South American progenitors.

PERU. Cajamarca: Prov. Cajamarca, 16 km W of Cajamarca up road (Avenida Peru) towards Cumbemayo, 3440 m, 31 Mar 1997, P.M. Peterson & N. Refulio Rodriguez 14010 (US, USM); 18 km W of Cajamarca up road (Avenida Peru) towards Cumbe Mayo, 3600 m, 31 Mar 1997, P.M. Peterson & N. Refulio Rodriguez 14013 (US, USM); 29 km from Cajamarca on road to Celendín, S.A. Renvoize & S. Lægaard 4974 (AAU, CPUN, K, US); Cumbe Mayo, I. Sánchez Vega & W. Ruiz Vigo 598 (CPUN), I. Sánchez Vega 4690 (CPUN); Cumbe Mayo, W of Cajamarca, S.A. Renvoize 5000, 5004 & 5005 S. Lægaard & I. Sánchez Vega (AAU, CPUN, K, US); Micuypampa, 62 km from Cajamarca towards Celendín, S.A. Renvoize & S. Lægaard 4961 (AAU, CPUN, K, US); Prov. San Miguel, 61 km N of Cajamarca on hwy 3N towards Bambamarca, 3640 m, 16 Mar 2000, P.M. Peterson & N. Refulio Rodriguez 14916 (CPUN, US, USM); Cajamarca to Celendín, 3 km NE of Encañada, I. Sánchez Vega 2777, V. Torrel & E. Medina (CPUN); S.A. Renvoize & S. Lægaard 4849 (CPUN). La Libertad: Prov. Bolivar, 3 air km ESE of Longotea on road to Bolivar, 3202 m, 31 Mar 2008, P.M. Peterson 21965, R.J. Soreng & J. Montoyo Quino (US, USM); Nevado Cajamarquilla, 3500 m, 9 Sep 1946, J. Infantes Vera 937 (MOL).

Caespitose perennials often sprawling, occasionally with stolons. Culms (10–) 25–55 cm long, glabrous below the nodes; internodes glabrous. Leaf sheaths mostly 0.8–8 cm long, shorter than the internodes, glabrous; ligules 1–2 mm long, apex acute, lacerate; blades 1.5–6 cm long, 0.5–2 mm wide, flat, scaberulous above, smooth beneath. Panicles 2–8 cm long, 0.5–1.2 cm wide, open, loosely-flowered with recemosely arranged branches; primary branches 2–4 mm long, excluding the awns, one per node, often purplish. Spikelet fasciles of three with one sessile or subsessile perfect spikelet and two short-pedicelled lateral spikelets staminate or sterile, the pedicels less than 0.2–0.5 mm long and the other two spikelets short-pedicelled, the pedicels about 0.7–1.2 mm long; glumes (1−)1.5–2.8 mm long, oblong and wider distally, 1-veined, apex deeply notched, awned, the awns 2–4 mm long, lobes triangular, acute; lemmas 2.5–3 mm long, fusiform, 3-awned, the central awns 5–13 mm long, lateral awns 2–3 mm long; paleas 2.5–3 mm long, puberulent, apex awned, the awns 1–2 mm long; anthers 1.6–1.8 mm long, yellowish to purplish. Caryopses 1−1.4 mm long, fusiform. 2n = 40, 60, 80.

Figure 5. 

A−D Muhlenbergia coerulea (Griseb.) Mez A habit B culm and panicle C ligule D spikelet E−K Muhlenbergia coerulea (Griseb.) Mez × Muhlenbergia rigida (Kunth) Kunth E culm and panicle F spikelet G floret H glumes I lemma J paleas, dorsal and ventral view K lodicules, stamens, and pistil. A−D drawn from P.M. Peterson, R.J. Soreng & J. Montoya Quino 21957 (US) E−K drawn from P.M. Peterson & N. Refulio Rodriguez 14860 (US).

Muhlenbergia cenchroides ranges from throughout México, Central America to South America in Bolivia, Brazil, Colombia, Ecuador, Peru, Guyana and Venezuela.

Muhlenbergia cenchroides occurs on rocky slopes, canyons, cliffs, roadcuts, arroyos, seeps and meadows associated Baccharis spp., Festuca myuros, Alnus, Polylepis, Fucaria, Salvia spp., Urochloa, Salvia spp., Calceolaria spp., Eupatorium, Festuca, Puya, Rubus, Schizachyrium, Cenchrus clandestinus, Calamagrostis spp., Muhlenbergia spp., Hyptis, Oxalis, Aristida, Begonia, Adiantum, Bidens, Lepechinia, Oreocallis grandiflora (Lam.) R. Br., Desmodium, Cortaderia bifida Pilg., Cortaderia jubata (Lemoine ex Carriere) Stapf, Sporobolus, Monnina, Carex, Cheilanthes, Eragrostis, Lupinus, Lycopodium, Jarava, Nassella, Werneria, Agave, Eucalyptus, Thalictrum and Chusquea; 1430–3850 m. Flowering December through September.

Muhlenbergia cenchroides can be separated from M. bryophilus in having anthers 1.6−1.8 mm long, the perennial habit with (10–) 25–55 cm tall culms and sessile or inconspicuously pedicelled perfect spikelets usually associated with two staminate or sterile pedicelled spikelets (Tovar 1993; Giraldo-Cañas and Peterson 2009).

Muhlenbergia cenchroides lies in a clade with M. tarahumara, M. uniseta and M. bryophilus in M. subg. Muhlenbergia (Fig. 1B; Peterson et al. 2010b). The multiple sampled individuals of M. cenchroides and M. uniseta in the current analyses do not resolve into reciprocally monophyletic lineages, but one sublineage, including accessions of each species, is strongly supported. This strongly suggests gene flow among individuals of these two species.

Peru. Ancash: Prov. Bolognesi, Paramarca, cerros al E de Chiquián, 3680 m, 8 Apr 1952, E. Cerrate 1396 (MOL, USM); Prov. Carhuaz, Cordillera Negra, 22 km SW of Shupluy and Rio Santa, 9°17'19.7"S, 77°44'39.3"W, 3770 m, 13 Mar 2008, P.M. Peterson 21652, R.J. Soreng, M.I. La Torre & J.V. Rojas Fox (US, USM); Prov. Corongo, Cordillera Blanca, 3 km E of Yanac, 8°35'55.6"S, 77°50'4.8"W, 2849 m, 18 Mar 2008, P.M. Peterson & R.J. Soreng 21786 (US, USM); Prov. Corongo, Cordillera Blanca, E of Yungay, 3400 m, 5 Apr 1988, S.A. Renvoize & S. Lægaard 5055 (CPUN, K); Prov. Huaraz, W side of Cordillera Blanca, S of Quebrada Ishinca, 9°24'55.8"S, 77°32'45.8"W, 2885 m, 12 Mar 2008, P.M. Peterson 21614, R.J. Soreng, M.I. La Torre & J.V. Rojas Fox (US, USM); Prov. Huaraz−Recuay border, W side of Rio Santa Canyon, 19 km S of Huaraz, 9°40'58.1"S, 77°28'29.7"W, 3202 m, 11 Mar 2008, P.M. Peterson 21600, R.J. Soreng, M.I. La Torre & J.V. Rojas Fox (US, USM); Prov Huaylas, Cordillera Blanca, encima de Caraz, 3200 m, A Weberbauer 3234 (MOL); Prov. Huaylas, Huata, M.I. La Torre 2793 (USM); Prov. Pallasca, 17 km N of Huandoval and 6 km S of Pallasca, 3360 m, 27 Mar 1997, P.M. Peterson & N. Refulio Rodríguez 13927 (US, USM); 3.4 km N of Huandoval towards Huascaschuque, 8°18'59.5"S, 77°58'9.5"W, 2949 m, 21 Mar 2008, P.M. Peterson & R.J. Soreng 21817 (US, USM); Prov. Huari, near Laguna de Puruhay, M.I. La Torre 3692 (USM); San Marcos, A. Cano 13505 (USM); Huascarán National Park, Quebrada Rurichinchay, D. Smith 12659, A. Gonzales & D. Maldonado (USM); Prov. Recuay, Cordillera Blanca, 16 km E of Catac on road towards Chavin de Huantar, 3630 m, 21 Mar 1997, P.M. Peterson & N. Refulio Rodríguez 13833 (US, USM); Prov. Yungay, Cordillera Blanca, 20 km ENE of Yungay, 9°6'26.2"S, 77°41'8.2"W 3247 m, 15 Mar 2008, P.M. Peterson 21712, R.J. Soreng, M.I. La Torre & J.V. Rojas Fox (US, USM); Quebrada Llauganuco, 24 km ENE of Yungay, 9°5'46.3"S, 77°40'19.3"W, 3309 m, 16 Mar 2008, P.M. Peterson 21739, R.J. Soreng, M.I. La Torre & J.V. Rojas Fox (US, USM); Prov. Yungay, Huascarán National Park, Llanganuco sector, María Josefa trail between Chinancocha and Pucayacu, 77°39'W, 9°05'S, 3700−3850 m, 7 May 1985, D.N. Smith 10512 (CPUN, MO). Ayacucho: Ayna, L. Aucasime 258 (USM); Seqseqa, L. Aucasime 81 (USM); Prov. Huanca Sancos, 27 km NW of Putajasa and 3 km S of Sacsamarca, 13°57'51.1"S, 74°18'41.5"W, 3650 m, 25 Feb 2002, P.M. Peterson 16278, A. Cano, M. I. La Torre, A. Ramirez & D. Susanibar Cruz (US, USM). Cajamarca: near Cajamarca, 2700 m, 11 Mar 1986, B, Becker & F.M. Terrones H. 601 (LPB); Cajamarca to Celendín, 95 km from Cajamarca, above Quillimbas, 3000 m, 22 Mar 1988, S.A. Renvoize & S. Lægaard 4868 (CPUN, K); Prov. Cajamarca, 16 km W of Central Plaza of Cajamarca up road towards Cumbemayo on Avenida Peru, 3440 m, 31 Mar 1997, P.M. Peterson & N. Refulio Rodríguez 14012 (US, USM); Prov. Cajamarca, Dist. Baños del Inca, Tres Tingos, margen Oeste del río Chonta, 2900 m, 2 Mar 2002, I. Sánchez Vega 11261 (CPUN); Prov. Cajamarca, Cerro Huairapongo–Baños del Inca, 19 Nov 1965, I. Sánchez Vega 126 & Julio Mercado (CPUN); Prov. Cajamarca, Fundo Aylambo, a 5 km antes de la ciudad, 8 May 1969, I. Sánchez Vega 385 & W. Ruiz Vigo (CPUN); Prov. Cajamarca, cerca al Paso El Gavilán, 3100 m, 19 Apr 1975, I. Sánchez Vega 1407, P. Brandelard & J. Sanabria (CPUN); Prov. Cajamarca, Laguna de Moyococha, 2550 m, 29 Aug 1965, I. Sánchez Vega 92 (CPUN); Prov. Cajamarca, Dist. San Juan, lugar Huacraruco, 2350 m, 19 Jun 1993, J. Cabanillas S. & J. Guevara B. 615 (CPUN); Chotén, en el Arboretum de CICAFOR, a 4 km de la carretera Pacasmayo–Cajamarca, 2990 m, 23 May 1981, I. Sánchez Vega 2562, V. Torrel & E. Medina (CPUN); Prov. Cajamarca, Dist. Cajamarca. Paso El Gavilán, 3100 m, 26 Jun 1966, I. Sánchez Vega 239 (CPUN); Prov. Cajamarca, ladera que converge al Valle Cajamarca, Lla Colpa, 2900 m, 22 Apr 1975, I. Sánchez Vega 1416, P. Brandelard, J, Sanabria & W. Ruiz Vigo (CPUN); Prov. Cajamarca, Sais Atahualpa de Porcón, en el Arboretum de CICAFOR, 3400 m, 16 May 1981, I. Sánchez Vega 2512, V. Torrel P. & E. Medina (CPUN); Prov. Cajamarca, Dist. Namora, Hacienda Polloquito, 3000 m, 6 May 1967, I. Sánchez Vega 321 (CPUN);12 km N of Cajamarca on road towards Bambamarca, 3020 m, 14 Mar 2000, P.M. Peterson & N. Refulio Rodríguez 14855 (CPUN, US, USM); S of Paso El Gavelan, 10 air km S of Cajamarca, 7°15'37.2"S, 78°30'34.5"W, 2544 m, 26 Mar 2008, P.M. Peterson 21875, R.J. Soreng & I. Sánchez Vega (US, USM); cumbre El Gavilán, R. Ferreyra 3255 (USM); Prov. Celendin, 4 air km W of Celendin, 6°54'13.5"S, 78°10'8.4"W, 2687 m, 29 Mar 2008, P.M. Peterson 21925, R. J. Soreng & J. Montoya Quino (US, USM); Prov. San Ignacio, 31 km E of Sondor on road towards Tabaconas, 2490 m, 31 Mar 2000, P.M. Peterson & N. Refulio Rodríguez 15128 (CPUN, US, USM); Prov. San Miguel, Niepos, 2200 m, 30 Oct 1985, S. Llatas 1503 (CPUN); Prov. San Pablo, Dist. San Pablo, lugar El Molino, 2200 m, 12 Jun 1993, J. Sánchez Vega 663 (CPUN). Cusco: Prov. Calca, Manto a Amparaes, 2650 m, 18 Apr 1966, C. Vargas C. 17393 (LPB); Prov. Cusco, Socorro−K’inka, C. Vargas C. 13161 (USM); Ruinas de Sacsahuamán, 3500 m, 6 May 1983, S.G. Beck 8365 (LPB); Mandor, abajo de Machupicchu, 2000 m, 13 Apr 1957, H. Ellenberg 988 (LPB); Cusco−Huancaro hwy, P. Gutte & G. Muller 9425a (USM); Machupicchu, camino entre la ciudad inca de Machupicchu y el Puente del Inca, 2000 m, 18 Sep 2004, D. Giraldo-Cañas 3759 (COL). Huancavelica: Prov. Huancavelica, Huando, O. Tovar 1254 (USM). Huánuco: Prov. Huánuco, Carpish, cumbre entre Huánuco y Tingo María, 2700 m, 1 Oct 1950, R. Ferreyra 8070 (MOL); Prov. Huánuco, Carpish, cumbre entre Huánuco y Tingo María, R. Ferreyra 10022 (USM); 48.6 km NE of Huánuco towards Tingo María, T. Plowman & P.M. Rury s.n. (USM); Prov. Pachitea, 21 air km ENE of Huánuco, 9°51'53.1"S, 76°2'55.1"W, 2498 m, 6 Mar 2007, P.M. Peterson 20341, R.J. Soreng & K. Romaschenko (US, USM); Canyon of the Rio Grande, 44 air km E of Huánuco, P.M. Peterson 20363, R.J. Soreng & K. Romaschenko (US, USM). Junín: Prov. Huancayo, near Paián, O. Tovar 9311 (USM); Cerro al E de Huancayo, 3900 m, 2 May 1954, O. Tovar 2173 (US, USM); Prov. Tarma, entre Huancapistana, 2200 m, A. Weberbauer 2042 (MOL). La Libertad: Prov. Bolivar, entre el desvío a Uchumarca y Santa Luisa, 7°04'S, 77°49'W, 3700 m, 11 Nov 2001, I. Sánchez Vega 11194, M. Dillon & G. Iberico (CPUN); Prov. Bolivar, E side of Cerro Salumpuy, 8 air km NW of Bolivar, 7°7'39.2"S, 77°46'9.9"W, 3390 m, 30 Mar 2008, P.M. Peterson 21942, R. J. Soreng & J. Montoya Quino (US, USM); 3 air km ESE of Longotea on road to Bolivar, 7°3'27.9"S, 77°51'2.2"W, 3202 m, 31 Mar 2008, P.M. Peterson 21961, R. J. Soreng & J. Montoya Quino (US, USM). Lambayeque: Prov. Ferreñafe, Inkawasi, S. Llatas Quiroz 4122 (USM). Pasco: Prov. Oxapampa, Río Boqueria, 26 km from Oxapampa via Río Yamaquizu, D. Smith 1807, A. Pretel & L. Acosta (USM). Piura: Prov. Huancabamba, Porculla, 2200 m, 10 May 1992, S. Llatas Quiroz & H. De la Cruz S. 3098 (CPUN). San Martín: Prov. Mariscal Cáceres, puerto de Norte de Río Abiseo, A. Cano 7466, B. Young & J. Roque (USM).

Sprawling, slender annuals. Culms 8–30 (−50) cm tall, glabrous, filiform, often tufted, freely branching at lower nodes; 0.2–0.5 mm diameter just below the inflorescence; internodes 6–42 mm long. Leaf sheaths (8−) 20–44 mm long, glabrous or sparsely pilose along the margins, shorter than the internodes; ligules 0.2–0.8 mm long, a ciliate membrane; apex truncate; margin with a tuft of hairs up to 1 mm long; blades 1–4 cm long, 0.6–1.4 mm wide, flat or loosely involute, often sparsely pilose above, glabrous below. Panicles 4–12 cm long, 1.8–5.0 cm wide, terminal, densely flowered; primary branches 1.5–3.7 cm long spreading and reflexed at maturity up to 90° from the rachises, one per node; pedicels 0.5–3 mm long, glabrous, appressed, erect; nodes 6–13 per panicle; Spikelets appressed to the branches, overlapping; glumes 0.7–1.7 mm long, subequal, glabrous, 1-nerved; apex acuminate, often mucronate; the mucro up to 0.5 mm long; lower glumes 0.7–1.5 mm long; upper glumes 0.8–1.7 mm long; lemmas 1.8–2.5 mm long, lanceolate, slender, awned, strongly 3-nerved but appearing five-nerved, the intermediate “nerves” actually rows of short barbs on top of folded epidermal ridges, sometimes with prominent short hairs (scabers) along the lateral nerves, often appearing glabrous without magnification, awns 5–11(−18) mm long, flexuous; callus minutely short pubescent; paleas 1.6–2.4 mm long, narrowly lanceolate, glabrous; anthers 0.3–0.5 mm long, yellowish. Caryopses 0.8–1.8 mm long, narrowly fusiform, brownish. 2n = 20.

Muhlenbergia ciliata is found throughout México and Central America in Ecuador, Peru, Brazil, Bolivia, Brazil and Argentina.

Muhlenbergia ciliata is found on moist to dry soils usually beneath taller vegetation, sandy drainages, steep rocky slopes, rock outcrops and disturbed roadsides in woodlands with Acacia, Agave, Andropogon, Bidens, Baccharis spp., Bothriochloa, Eupatorium, Melinus minutiflora P. Beauv., Muhlenbergia bryophilus, M. flexuosa, M. rigida, Puya and Salvia; 1000–2400 m.

Muhlenbergia ciliata is morphologically similar to M. romaschenkoi and can be differentiated from the latter in having short ligules 0.2−0.8 mm long [1.2−3.0 (−5.0) mm long in M. romaschenkoi], paleas that are glabrous between the veins on the proximal ½ (versus appressed pubescent), 6−13 nodes along the panicle (versus 15−23) and panicles that are 4−12 cm long (versus 7−15 cm long) [Peterson and Giraldo-Cañas 2011, 2012]. Some individuals of M. ciliata from Peru do not have prominent cilia along the lateral veins that are present in most individuals from North America.

Muhlenbergia ciliata is closely related to M. pectinata C.O. Goodd. (North America) and M. tenella (Kunth) Trin. (North America, Central America and Colombia) [Peterson and Annable 1991]. These three species form a clade in Muhlenbergia subg. Muhlenbergia (Peterson et al. 2010b; Fig. 1B).

Peru. Amazonas: Piedra Grande, near Rio Santo Domingo, 5000 ft alt., 14−19 May 1923, J.F. Macbride 3684 (F, US). Cusco: Urubamba, Ruinas de Macchu Picchu, 2500 m, 27 May 1963, D. Ugent 5356 (US), 2300 m, 11 Apr 1963, C. Vargas C. 14354 (US), Mar 1987, I. Grignon 2306 (AAU, US); Quebrada Termas Macchu Picchu, 25 Mar 1966, C. Vargas C. 17145 (USM). Huánuco: 21 air km NE of Pachitea, 7 km E of Puerto Rancho junction, 9°49'45.9"S, 76°3'12.9"W, 2094 m, 6 Mar 2007, P.M. Peterson, R.J. Soreng & K. Romaschenko 20336 (US); Pachitea, canyon of the Rio Grande, along trail 1 air km NW of Estación Huacachay, 9°50'44.7"S, 75°50'5.2"W, 2323 m, 8 Mar 2007, P.M. Peterson, R.J. Soreng & K. Romaschenko 20378 (US); 2 air km ESE of Eastación Huacachay, 9°51'34.7"S, 75°50'48.1"W, 1867 m, 7 Mar 2007, P.M. Peterson, R.J. Soreng & K. Romaschenko 20359 (US). Junín: between Tarma and La Merced, 3000 m, 14 Oct 1923, A.S. Hitchcock 22154 (US); Mito, 9000 ft alt., 8−18 Apr 1923, J.F. Macbride 3376 (F, US); Province Huancayo, abajo de Pariabuena, 2000 m, 6 May 1969, O. Tovar 7936 (USM). La Libertad: Bolivar, W of Longotea ca. 0.5 km towards San Vicente on Balsas−Longotea road, 7°2'35.6"S, 77°52'39.8"W, 2487 m, 31 Mar 2008, P.M. Peterson, R.J. Soreng & J. Montoya Quino 21967 (US).

Densely caespitose perennials. Culms 50−100(−120) cm tall, erect, rigid, hirsute below the basal, terete nodes; usually 1 node per culm; internodes mostly glabrous and scabrous. Leaf sheaths mostly 5−18 cm long, glabrous to scaberulous above, rounded near base, lower sheaths often becoming fibrous with age; ligules 8−15 mm long, firm below, strongly decurrent, often lacerate, apex obtuse to acute; blades 15−35(−45) cm long, 2−5 mm wide, tightly involute, glabrous to scaberulous below mostly scaberulous near above. Panicles (6−)10−24(−30) cm long, 6−15 mm wide, narrow, spike-like, usually plumbeous; primary branches 0.2−2.5 cm long, erect and tightly ascending appressed, floriferous to base; pedicels 0.5−4 mm long, usually shorter than the spikelets, hispid. Spikelets 5−7(−8) mm long, plumbeous, rarely 2-flowered; glumes (4−)5−7(−8) mm long, usually as long or longer than the floret, sometimes a little shorter, lanceolate, about equal, 1-nerved, scabrous, apex acuminate, unawned, mucronate, or short-awned; lemmas (4.6−)5−6.7(−7.1) mm long, lanceolate, plumbeous, scabrous, apex acuminate, unawned, mucronate or short-awned, the awn 1−3(−4) mm long, inserted just below the apex; callus sparsely short bearded, the hairs 0.1−0.2 mm long; paleas (4.6−)5−6.5 mm long, about as long as the lemma, narrowly lanceolate, scaberulous, apex acuminate; anthers 2−3 mm long, purplish or yellowish. Caryopses 2.5−3.5 mm long, fusiform, dark reddish-brown.

Figure 6. 

A−C Muhlenbergia coerulea (Griseb.) Mez A habit B panicle C spikelet D−F Muhlenbergia rigida (Kunth) Kunth D habit E panicle F spikelet. Drawings from Giraldo-Cañas and Peterson (2009), Peterson and Giraldo-Cañas (2011). A−C drawn from S.G. Beck 7700 (LPB) D drawn from P.M. Peterson 9659 (US) E, F drawn from P.M. Peterson, C.R. Annable & J. Valdés-Reyna 10876 (US).

Muhlenbergia coerulea ranges throughout the Andean Cordillera from Colombia, Venezuela, Ecuador to Argentina, Peru and Bolivia.

Muhlenbergia coerulea grows on rocky, often sandy slopes, derived from volcanic origins usually near arroyos associated with of Alnus, Anatherostipa obtusa (Nees & Meyen) Peñail., Aristida, Calamagrostis, Calceolaria, Festuca, Hypericum, Jarava ichu Ruiz & Pav., Lupinus, Monnina, Nassella, Oreocallis grandiflora (Lam.) R. Br., Polylepis, Puya, Rubus, Schizachyrium and cultivated Pinus; 2450−4900 m. Flowering February through August.

In recent literature (Giraldo-Cañas and Peterson 2009; Peterson and Giraldo-Cañas 2011, 2012), this species was referred to as Muhlenbergia angustata (J. Presl) Kunth but the type [Podosemum angustatum J. Presl] clearly aligns with what we had been referring to as the hybrid between this species and M. rigida. Therefore, we adopt the next available name, Muhlenbergia coerulea and change the hybrid designation to M. coerulea × M. rigida. Many specimens studied are intermediate between M. coerulea and M. rigida. These are treated as hybrids [M. coerulea (Griseb.) Mez × M. rigida (Kunth) Kunth; Lægaard and Peterson 2001; Peterson and Giraldo-Cañas 2011, 2012] since the size, width and colour of the panicles and the surface structure and length of the glumes and lemmas, are intermediate between these two recognised species.

Muhlenbergia coerulea is deeply embedded in the M. subg. Trichochloa clade, a group of tall, rather robust perennials historically placed in Podosemum or Epicampes (Soderstrom 1967; Peterson et al. 2010b; Fig. 1A).

Peru. Ancash: Prov. Huaylas, Pueblo Libre, Antircán, A. Cano 11714 (USM); Prov. Huari, Huascarán National Park, Quebrada Pachachaca, D.N. Smith 12619, A. Gonzalez & D. Maldonado (USM); Quebrada Los Cedros, D.N. Smith 9892, R. Valencia & L. Minaya (CPUN); Prov. Huari, Huascarán National Park, Alpamayo−Cashampampa trail, 3950 m, 13 Mar 1985, D.N. Smith 10054 & R. Valencia (MO, USM); Prov. Recuay, between Pequipalpa and Rachacoco, L.I. Masías 44 (USM); Huascarán National Park, Auqispuquipio, D.N. Smith 12115, R. Valencia & M. Buddensiek (MO, USM); Prov. Yungay, Cordillera Blanca, 20 km ENE of Yungay, 9°6'26.2"S, 77°41'8.2"W, 3247 m, 15 Mar 2008, P.M. Peterson 21703, R.J. Soreng, M. La Torre & J.V. Rojas Fox (US, USM); quebrada Llauganuco, 24 km ENE of Yungay, 9°5'46.3"S, 77°40'19.3"W, 3309 m, 16 Mar 2008, P.M. Peterson 21720, R.J. Soreng, M. La Torre & J.V. Rojas Fox (US, USM). Arequipa: Prov. Caraveli, Quicacha, 5 May 1955, A. Guevara s.n. (USM). Ayacucho: Prov. Huanca Sancos, 19 km NW of Putajasa on road towards Huanca Sancos, 14°00'2.6"S, 74°17'14.1"W, 3900 m, 25 Feb 2002, P.M. Peterson 16268, A. Cano, M. La Torre, A Ramirez & D. Susanibar (US, USM). Cajamarca: Prov. Cajabamba, ca. 20 km WSW of Cajabamba, 7°42'18.0"S, 78°14'1.5"W, 3263 m, 23 Mar 2008, P.M. Peterson & R.J. Soreng 21868 (US, USM); Prov. Cajamarca, La Encañada, Cerro Negro, M. Cabanillas Medina & M. Sánchez Montoya 1530 (CPUN); La Encañada, ruta Combayo−Yanacocha, I. Sánchez Vega 10574 (CPUN); N del canal Cumbe Mayo, I Sánchez –Vega U. Molau 3733 (CPUN); Cumbe Mayo, W of Cajamarca, S.A. Renvoize 4990, S. Lægaard & I. Sánchez Vega (CPUN, K, US); Pampas de Guanico, ruta a Guagal, I. Sánchez Vega 1141 (CPUN); Sais Atahualpa, de Porcón, I Sánchez Vega 2528, V. Torrel & E. Medina (CPUN); Quebrada de la Esperanza along road to Cumbe Mayo, I. Sánchez Vega & V. Torre 3289 (CPUN); Cerro Campanario, I. Sánchez Vega 6605 (CPUN); Prov. Celendin, Celendin, 3600 m, 24 Jun 1961, R. Ferreyra 15117 (USM); Prov. San Miguel, 64 km N of Cajamarca and 3 km SW of El Cobro, 3530 m, 16 Mar 2000, P.M. Peterson & N. Refulio Rodriguez 14926 (CPUN, US, USM); Prov. San Pablo, 32 km NW of Cajamarca towards San Pablo, 3470 m, 15 Mar 2000, P.M. Peterson & N. Refulio Rodriguez 14882 (US, USM); Cajamarca−Chota road, km 37−40 marker, A. Gentry 61575, C. Diaz & C. Blaney (MO, USM). Huancavelica: Prov. Huancavelica, Canyon of Rio Ichu, SW of Huancavelica, 12°48'48.2"S, 75°3'24.5"W, 4894 m, 14 Mar 2007, P.M. Peterson 20462, R.J. Soreng, K. Romaschenko & D. Susanibar (US, USM); Tayacaja, Hacienda Tocas, between Colcabamba and Paucarbamba, 3400 m, 20 Apr 1954, O. Tovar 1981 (US, USM). Huánuco: Prov. de Huánuco, Mitotambo, above Mito, R. Ferreyra 6895 (MOL, US, USM); above Mitotambo, R. Ferreyra 9434 (USM); 3−6 mi NW of Mito, J.F. Macbride and Featherstone 1929 (F, US), Mito, J.F. Macbride and Featherstone 1721 (F, US); Prov. Ambo, Huarmiragra, A. Granda 1676 (USM). Junín: Pachacaya−Huari, 3600 m, 25 Mar 1979, O. Tovar 7838 (USM); Prov. Huancayo, Cerros E of Huancayo, O. Tovar 3259 (US); above Ocopilla, near Huancayo, O. Tovar 4506 (US, USM); above Huancayo, O. Tovar 2795 (US, USM); Palián, O. Tovar 9339 (USM); Cerros E of Huancayo, O. Tovar 3259 (USM); Oroya, A.S. Hitchcock 22182 (US). La Libertad: Prov. Huancayo, Acopalca, 4000 m, 20 Jul 1945, J. Infantes Vera 406 (LIL); Prov. Bolivar, 3 km ESE of Longotea and 9 km W of Uchumarca, 7°3'27.9"S, 77°51'2.2"W, 3202 m, 31 Mar 2008, P.M. Peterson 21957, R.J. Soreng & J. Montoya Quino (US, USM); Prov. Otuzco, Trujillo−Huamachuco road, 10−15 km before Shorey, D.N. Smith & R. Vasquez 3289 (MO, USM); Larbimbambu, 2450 m, 5 Feb 1949, J. Infantes Vera 1654 (LIL); Cerro Sango, A. Sagástegui 14428 (HAO); Prov. Santiago de Chuco, Shoreyo−Truillo road, 5 km from Shoreyo, D. Smith 2339 (MO, US, USM). Lambayeque: Prov. Ferreñafe, Incahuasi, S. Llatas Q. 1934 (CPUN, HAO, USM). Piura: Prov. Huancabamba, 14 km E of Sondor on road towards Tabaconas, 2540 m, 31 Mar 2000, P.M. Peterson & N. Refulio Rodriguez 15153 (CPUN, US, USM). Puno: Chijnaya, Pueblo de Pucará, 3900 m, Mar 1964, A. Vera 107 (COL); Hacienda Caracara, entre Llave y Pucará, 3850 m, 4 Mar 1966, O. Tovar 5162 (US); Hacienda Sollocota, 3850 m, 7 Mar 1966, O. Tovar 5229 (USM); Camacani, 9 Mar 1966, 3850 m, O. Tovar 5263 (USM); Prov. Carabaya, 10 km S of Ollachea, J.D. Boeke & S. Boeke 2974 (NY, US); Prov. Chucuito, 3 km S of Pizacoma, 4050 m, 7 Mar 1999, P.M. Peterson & N. Refulio Rodriguez 14694 (US, USM).

Panicles (−0.6)1−4 cm wide, spike-like with lower branches slightly prolonged, erect, plumbeous to reddish-purple. Spikelets plumbeous to reddish-purple, scabrous; glumes 2.5−3.5(−4) mm long, ½ to ¾ as long as the floret; lemmas 4−6 mm long, awned, the awns generally 3−8(−10) mm long, straight.

This presumed hybrid is known to occur in Argentina, Chile, Colombia, Ecuador, Peru and Venezuela.

The hybrid occurs on gravelly slopes and near cultivated fields in many different plant communities between 2200−3800 m in association with Alnus, Aristida adscensionis L. Baccharis, Berberis, Calceolaria, Cenchrus clandestinus, Eragrostis pastoensis (Kunth) Trin., Festuca, Jarava, Lantana, Lupinus, Muhlenbergia cenchroides, M. phalaroides, M. rigida, Oxalis, Polygala, Puya, Schinus molle L., Schizochyrium and Solanum.

As expected, individuals of M. coerulea × M. rigida have an intermediate morphology, such as: lemma awn length [3−8 (−10) mm], glume length (1/2−3/4 as long as the lemma) and spikelet colouration (plumbeous to reddish-purple). In the Flora of Ecuador, Lægaard and Peterson (2001) recognised two intermediate forms (“intermediate” and “subangustata”) based on lemma awn length, glume length, colour of the spekelets and surface scabrosity of the glumes and lemmas.

There are no molecular studies investigating the population genetics of the hybrid with both presumed parents but we hope to persue this in the future. In our analysis, two samples of M. coerulea from Peru form a pair with little variation and two samples of M. rigida, one from Mexico and the other from Peru, form a pair with little variation in the analysis of seven DNA sequence markers (Peterson et al. 2010b). Each of these two clades of M. coerulea and M. rigida were not paired but were placed along a comb-like grade in the M. subg. Trichochloa clade. In our new analysis, there are more samples of M. rigida from Mexico and there is greater genetic variability among individuals of this species (Fig. 1). However, overall there appears to be low levels of divergence among species in M. subg. Trichochloa, hence the comb-like appearance suggesting rapid speciation (Peterson et al. 2010b).

Peru. Ancash: 10 km towards Casma, S.A. Renvoize & S. Lægaard 5154 (CPUN); E of Yungay, S.A. Renvoize & S. Lægaard 5058 (CPUN); Prov. Asunción, Chacas, A. Cano 14572, M. La Torre & W. Mendoza (USM); Prov. Bolognesi, above Chiquián, E. Cerrate 1549 (US, USM); Prov. Corongo, Ocshmarca, S. Leiva 51 (USM); Prov. Huaylas, Huascarán National Park, Auquispuquio ruins, D.N. Smith 11960, R. Valencia & M. Buddensiek (CPUN, USM); Huascarán National Park, Pueblo Libre, A. Cano 11619 (USM); Pueblo Libre, Antircán, A. Cano 11714 (USM). Apurimac: Prov. Abancay, 48 km SW of Abamcay on road towards Andahuaylas, 13°42'23.6"S, 72°57'20.3"W, 3280 m, 21 Mar 2002, P.M. Peterson & N. Refulio Rodriguez 16650 (US, USM). Ayacucho: Prov. Huamanga, 23 km S of Ayacucho on hwy 3 towards Abancay, 13°16'21.5"S, 74°13'46.8"W, 3575 m, 15 Mar 2007, P.M. Peterson 20490, 20496, R.J. Soreng, K. Romaschenko & D. Susanibar Cruz (US, USM); 27 km S of Ayacucho on hwy 3 towards Abancay, 13°17'9.8"S, 74°13'41.9"W, 3684 m, 16 Mar 2007, P.M. Peterson 20502, R.J. Soreng, K. Romaschenko & D. Susanibar Cruz (US, USM); Prov. Huanca Sancos, 23 km NW of Putajasa on road towards Huanca Sancos, 13°58'11.1"S, 74°18'9.0W, 3800 m, 25 Feb 2002, P.M. Peterson 16272, A. Cano, M. La Torre, A Ramirez & D. Susanibar (US, USM); Prov. Huanca Sancos, 27 km NW of Putajasa and 3 km S of Sacsamarca, 13°57'51.1"S, 74°18'41.5"W, 3650 m, 25 Feb 2002, P.M. Peterson 16273B, A. Cano, M. La Torre, A Ramirez & D. Susanibar (US, USM); Prov. Lucanas, 13 km E of Puquio at km 172 marker, 14°41'18.5S, 74°4'26.8W, 3730 m, 8 Apr 2004, P.M. Peterson & N. Refulio Rodriguez 18207 (US, USM); Ancamarca, L. Vargas & G. Mora 337 (USM). Cajamarca: Prov. Cajamarca, 12 km N of Cajamarca on road toward Bambamarca, 3020 m, 14 Mar 2000, P.M. Peterson & N. Refulio Rodriguez 14860 (CPUN, US, USM); Cajamarca−Bambamarca, 13−18 km from Cajamarca, D.N. Smith & R. Vasquez M. 3441 (MO, US, USM); Chotén, 4 km de la carretera Pacasmayo, I. Sánchez Vega 2570, V. Torrel & E. Medina (CPUN); Porcón, I. Sánchez Vega 51 (CPUN, US); above La Encañada ruta a Celendín, I. Sánchez Vega & W. Ruiz Vigo 1730 (CPUN); Prov. Celendín, La Tranca, I. Sánchez Vega & W. Ruiz Vigo 1815 (CPUN); Prov. Celendín, 4 air km W of Celendín, 6°54'13.5"S, 78°10'8.4"W, 2687 m, 29 Mar 2008, P.M. Peterson 21921 & 21922, R.J. Soreng & J. Montoya Quino (US, USM); 10 km from Celendín towards Rio Marañon, S.A. Renvoize & S. Lægaard 4883 (CPUN); Celendín to Cajamarca, near Quillimbas, S.A. Renvoize & S. Lægaard 4871 (CPUN); Cerro Conturami 10 km from Celendín, S.A. Renvoize & S. Lægaard 4946 (CPUN); Prov. Contumaza, Tres Cruces, A. Sagástegui & M. Fukushima 5119 (US); Celendín−Balsas road, 3−10 km from Celendín, D.N. Smith & I. Sánchez Vega 4300 (MO, US). Cusco: Prov. Calca, 10 km N of Calca on road towards Lares, 13°16'2.9"S, 71°55'20.1W, 3490 m, 17 Mar 2002, P.M. Peterson & N. Refulio Rodriguez 16597 (US, USM); Prov. Santo Tomas, Chumbivilcas, Apr 1982, M.E. Tapia 208 (USM). Huancavelica: Motcca, cerca a Conaica, 3500 m, 1 Apr, 1967, O. Tovar 5889 (USM); Prov. Huancavelica, Pararpuquio, below Conaica, O. Tovar 169 (MOL, US, USM); Sachahuajta, 7 km to Conaica, O. Tovar 950 (US, USM); near Yauli, O. Tovar 2996 (US, USM); Yacu−huanay, O. Tovar 3695 (USM, US); Prov. Tayacaja, Andaimarca, between Colcabamba and Surcubamba, O. Tovar 1821 (US, USM). Huánuco: Prov. de Huánuco, Mitotambo above Mito, R. Ferreyra 9477 (US, USM); Mito, J.F. Macbride 3320 (F, US). Junín: Prov. Huancayo, Paccba, 20 km S of Huancayo, O. Tovar 3294 (US, USM); Cerro La Libertad, O. Verlarde Nuñez 2637 (MOL). La Libertad: Prov. Bolivar, above Longotea, ruta Bolivar, I. Sánchez Vega 5015 (CPUN); Prov. Otuzco, Agallpampa, A. López M. 1041 (US); Trujillo−Huamachuco road, D.N. Smith & R. Vasquez 3309 (MO, USM). Lambayeque: Prov. Ferreñafe, Inkawasi, S. Llatas Quiroz 4114 (USM). Lima: Prov. Canta, 2 km SE of San Jose Canta, 11°30'2.0"S, 76°40'23.4W, 2232 m, 27 Mar 2004, P.M. Peterson & N. Refulio Rodriguez 17984 (US, USM). Piura: 14 km E of Sondor on road towards Tabaconas, 2540 m, 31 Mar 2000, P.M. Peterson & N. Refulio Rodriguez 15160 (CPUN, US, USM).

Mexico, Porto Pedro, Karwinsky 1393 (holotype: LE-TRIN-1497.01!; isotypes: US-84831! fragm. ex LE-TRIN-1497.02, W!).

Sprawling annuals. Culms 16–50 cm tall, decumbent, rooting at the lower nodes; nodes retrorsely pilose; internodes smooth or scabridulous. Leaf sheaths 1.5–8.5 cm long, sparsely or densely pilose, hairs to 3 mm long, papillose-based; ligules 0.5–0.8 mm long, membranous, apex truncate, erose; blades 2–6 cm long, 1.5–4 mm wide, flat, bases distinctly narrowed to the junction with the sheath, surfaces scabridulous and sparsely pilose, hairs papillose-based. Panicles 6–10.5 cm long, 2.0–4.5 cm wide, secund, open; primary branches 0.8–3.5 cm long, secund, spreading at right angles or somewhat reflexed usually lying to one side with 2–5 spikelets; secondary branches not developed; pedicels 1–5 mm long, scabrous or shortly pilose, hairs papillose-based; disarticulation at the base of the primary branches where there is a weak and contorted stipe. Spikelets 4–8 mm long, dimorphic with respect to the glumes, proximal spikelets on each branch almost sessile; glumes of proximal spikelets on each branch subequal, 0.2–0.7 mm long, orbicular, truncate, often erose or irregularly toothed, unawned; glumes of distal spikelets on each branch markedly unequal; lower glumes to 8 mm long, 1-veined, acute, usually awned, awns 0.5–3 mm; upper glumes orbicular, acute, sometimes awn-tipped; lemmas 4.0–7.6 mm long, linear to broadly lanceolate, light greenish, smooth or scabrous, usually with greenish veins, apices acuminate, awned, awns 6–19 mm long, usually straight, scabrous; paleas 3.7–6.8 mm long, narrowly lanceolate, coarsely papillate or almost smooth, 2-keeled, the veins prominent, scabrous, greenish, sometimes extending as minute awns, acuminate; anthers 0.4–0.8 mm long, yellowish. Caryopses 1.8–3 mm long, oblong-ovoid, flattened, brownish. 2n = 20.

Figure 7. 

A−D Muhlenbergia diversiglumis Trin A habit B ligule C glumes D floret E−H Muhlenbergia microsperma (DC.) Kunth E habit F ligule G glumes H lemma. Drawings from Peterson and Annable (1991)A−D drawn from P.M. Peterson & C.R. Annable 4158 (WS) F−H drawn from P.M. Peterson & C.R. Annable 4185 (WS).

The species is native to North America, Central America, Colombia, Venezuela, Ecuador, Peru, and Argentina.

Muhlenbergia diversiglumis grows on moist cliffs, along water courses, sandy slopes, and road cuts, primarily in moist shaded environments of broadleaf evergreen forests and pine-oak forests, at elevations of 600–2500 m.

Muhlenbergia diversiglumis can be differentiated from M. ciliata, M. microsperma, and M. romaschenkoi in having secund panicles (versus not secund in the latter three species) with each primary branch consisting of 2–5 dimorphic spikelets where the proximal spikelets have short orbicular glumes less than 1 mm long, and the distal spikelets have glumes up to 8 mm long (Peterson and Annable 1991; Giraldo-Cañas and Peterson 2009).

Muhlenbergia diversiglumis is a member of M. subg. Muhlenbergia and is sister to M. alamosae Vasey and together they are sister to the M. tarahumara−M. cenchroides−M. bryophilus−M. uniseta clade (Fig. 1B).

Peru. Amazonas: Dist. Vista Alegre, Puente sobre el Río Salas, 1525 m, 30 Jun 1998, I.M. Sánchez Vega, M.O. Dillon & M. Zapata 9580 (HAO, MO). Ayacucho: Naranjayoc, entre Ayna y el Río Apurimac, 900 m, 16 May 1969, O. Tovar 6136 (USM); Ayna, cerca entre Tambo y San Francisco, Jan 1969, L. Aucasime 428 (USM); Province La Mar, Machente, entre Yanamonte y Ayna, 1200 m, 16 May 1969, O. Tovar 6126 (USM); Province La Mar, entre Ayna & Río Apurimac, 900 m, 16 May 1969, O. Tovar 6136 (USM); Ayna, between Huanta and Río Apurimac, 750 m, 7 May 1929, E.P. Killip & A.C. Smith 23127 (US). Cusco: Urubamba Valley, San Miguel, 1800 m, 28 May 1913, O.F. Cook & G.B. Gilbert 958 (US); Urubamba, Ciudadela Macchu Picchu, 2300 m, 11 Apr 1963, C. Vargas C. 2159 (US), 14355 (US, USM); Urubamba, Macchu Picchu, 2040 m, Mar 1949, F. Marin 1381 (US); Urubamba, 110 km de Cusco en el camino y atrás de las aguas termales con plantaciones de palta, Macchu Picchu, 2050 m, 21 May 1988; G. Valencia & R. Ochoa 9147 (MO, US). Huánuco: Province Leoncio Prado, La Divisoria, carretera a Pucallpa, 1600 m, 21 Apr 1989, J. Schunke Vigo 11349 (MO, US, USM). Piura: Huancabamba, Porculla, 1770 m, 6 Mar 1989, S. Llatas Quiroz 2431 (CPUN, HAO, MO).

Dense mat-forming perennials with scaly rhizomes, the acute scales 4.5−8.1 (−10) mm long, the rhizomes 1−2 (−2.5) mm in diameter. Culms 2−8 (−11) cm long, mostly erect, 2−3 (4) mm diameter below; internodes 1−10 mm long, compressed. Leaf sheaths 3−6 (−10) mm long, distichous, overlapping, margins hyaline; ligules 6−1.4 mm long, membranous, decurrent, apex acute to obtuse; blades 2.5−8.5 mm long, 0.6−1.1 mm wide, involute, arcuate, glabrous to finely papillose, margins scabrous, apex navicular, often pungent. Panicles 1−2 cm long, 1−5 mm wide, contracted, narrow, usually exserted with 3−9 nodes; primary branches 0.4−1 cm long, ascending, solitary at a node; rachis papillose-roughened just below the spikelets. Spikelets (1.8−-) 2−2.5 mm long, plumbeous; glumes (0.8−) 1−1.6 mm long,about ½ as long as the floret, subequal, 1-veined, rarely 2-veined, apex acute to obtuse; lemmas (1.7−) 1.9−2.4 mm long, 3-veined, glabrous, plumbeous, apex acute, mucronate, the mucros less than 0.3 mm long; paleas (1.6−) 1.8−2.4 mm long, 2-veined, glabrous; anthers 1−1.7 mm long, yellow or purple. Caryopses 1−1.3 mm long, about 0.4 mm wide, ellipsoid, dark brown.

Figure 8. 

A−E Muhlenbergia fastigiata (J.Presl) Henrard A habit B ligule C glumes D floret E stamens and pistil F−J Muhlenbergia ligularais (Hack.) Hitchc F habit G ligule H glumes I floret J stamens and pistil. Drawings from Giraldo-Cañas and Peterson (2009), Peterson and Giraldo-Cañas (2011)A−E drawn from P.M. Peterson, S. Lægaard, R.J. Soreng & C.R. Annable 12709 (US) F−J drawn from P.M. Peterson, S. Lægaard, R.J. Soreng & C.R. Annable 12684 (US).

Muhlenbergia fastigiata is found in South America in the Andean highlands of Argentina, Bolivia, Chile, Colombia, and Peru (Morden 1985; Morden and Hatch 1996).

Muhlenbergia fastigiata occurs on grassy flats, playas, slopes, rock outcrops, near gravelly creeks and lake margins in granitic and calcareous soils associated with Baccharis, Berberis, Calamagrostis, Ephedra, Festuca, Jarava, Margyricarpus, Muhlenbergia, ligularis, M. peruviana, and Nassella; 3000−4900 m.

Morphologically, M. fastigiata can sometimes be confused with the distantly related M. ligularis (M. subg. Bealia; Fig. 1B). However, the former has well developed rhizomes (absent in M. ligularis) and tightly involute, acuate leaf blades (versus flat and straight). Muhlenbergia richardsonis (Trin.) Rydb., a wide ranging North American species, is also morphologically similar to M. fastigiata in most characters, although M. richardsonis has a taller habit and differes in leaf anatomy (Morden 1985; Morden and Hatch 1996). Aciachne acicularis Lægaard and A. pulvinata Benth., two small, compact, mat-forming perennials, can also be mistaken for M. fastigiata. However, both species of Aciachne (Pooideae: Stipeae) have longer spikelets ranging from 3.8−6 mm long, glumes that are 3−5-veined, and tightly overlapping lemma margins (Renvoize 1998; Giraldo-Cañas and Peterson 2009).

Muhlenbergia fastigiata is sister to the North American, M. richardsonis in M. subg. Pseudosporobolus [Fig. 1; Peterson et al. 2010b].

Peru. Ancash: Recuay, Cordillera Blanca, 39 km S of Catac on road towards Raquia, 3980 m, 21 Mar 1997, P.M. Peterson 13825 & N. Refulio Rodriguez (US, USM); Cordillera Negra, E slope of Cerro Pullicharca (Purac), ca. 1.5 km W of hwy 109 and then 3.6 km S of Tapacocha along Rio Santa, 9°55'39.4"S, 77°23'45.3"W, 3822 m, 9 Mar 2008, P.M. Peterson 21512, R.J. Soreng, M.I. La Torre & J.V. Rojas Fox (US, USM); between Santa Rosa and Araranca 12 Apr 1915, O.F. Cook & G.B. Gilbert 168 (US). Arequipa: Prov. Caylloma, Valle de Colca, Chiray−Tuti, 3900 m, 12 Jan 1999, S.G. Beck 26354 (LPB); Prov. Caylloma, Pampa Cañahuas, “Grama dulce”, 4200 m, 3 Jul 2001, M. Rodríguez Diaz 1130 (USM). Cajamarca: Prov. Hualgayoc, 8 km NE of Hualgayoc on hwy 3N towards Bambamarca, 3080 m, 17 Mar 2000, P.M. Peterson & N. Refulio Rodriguez 14950 (CPUN, US, USM). Kanzel, above Sunchubamba, 3680 m, 6 Aug 1957, H. Ellenberg 1852 (US). Cusco: Chumbivilias, Rio de Velille, 3850 m, C. Vargas C. 14084 (US); Espinar, alrededores de Yauri, 3900 m, 26 Mar 1956, 26 Mar 1956, C. Vargas C. 11209 (US). Huancavelica: Huancavelica, Canyon of Rio Ichu, SW of Huancavelica ca. 5 km on Hwy 3 to Santa Ines and Ayacucho, 12°48'48.2"S, 75°3'24.5"W, 4894 m, 14 Mar 2007, P.M. Peterson 20463, R.J. Soreng, K. Romaschenko & D. Susanibar Cruz (US, USM); Tayacaja, Just above Chuquitambo, 4 km SW of Pazo, 3975 m, 9 Apr 1997, P.M. Peterson 14151 & O. Tovar (US, USM). Junín: Prov. Huancayo, Acopalca, 3900 m, 25 Jul 1945, J. Infantes Vera s.n. (LIL); Prov. Huancayo, Acopalca, 4000 m, 20 July 1947, J. Infantes Vera 446 (LIL); entre Tarma y La Oroya, 3700 m, A. Weberbauer 2525 (MOL); Hacienda Cachi-Cachi, 4000 m, 22 Oct 1950, O. Velarde Nuñez 2869 (MOL); Jauja, 34 km SE of La Oroya on road towards Jauja, 3600 m, 9 Apr 1997, P.M. Peterson 14125 & O. Tovar (US, USM); Jauja, Tarma−Jauja road, 28 km from Tarma, 11°35'S, 75°38'W, 3950 m, 10 Jan 1984, D.N. Smith 5694 (MO, US); Junín, SE shore of Lago Chinchay Cocha (Junin) and 8 km S of Huayre, 4110 m, 7 Apr 1997, P.M. Peterson 14096 & O. Tovar (US, USM); Yauli, 156 km W of Lima just above Yauli, 4120 m, 5 Apr 1997, P.M. Peterson 14040 & O. Tovar (US, USM); Yauli, La Oroya, 30 Nov 1924, F.L. Stevens 1 (US); Oroyo, 23 Oct 1923, A.S. Hitchcock 22135 (US), 21 Feb 1954, Hirsch s,n. (US), Stevens 1 (US); entre Tarma y Oroya, 3400 m, 29 Jun 1948, R. Ferreyra 3828 (MOL, US, USM); ca. 24 km W of Tarma, 4050 m, 6 May 1979, Teppner 79/387 (US). La Libertad: Prov. Huamachuco, Cangau Sartimbamba, 3200 m, 28 Jan 1952, J. Infantes Vera 4072 (LIL); Prov. Huamachuco, Cangau Sartimbamba, 4000 m, 29 Jan 1952, J. Infantes Vera 4045 (LIL); Prov. Huamachuco, Huailillas, 3800 m, 8 Aug 1951, J. Infantes Vera s.n. (LIL). Lima: Provincia Huarochiri, Chilca, Bella Vista, 3800 m, 5 Jun 1940, E. Asplund 11436 (NY, US); road from Lima to Huancayo, 3300 m, 20 May 1981, G. Sullivan, K. Young, S. Sánchez & D. Soejarto 1021 (MO, US). Pasco: Pasco, 8 km W of NW arm of Laguna de Junín, 10°55'51.9"S, 76°18'8.6"W, 4141 m, 5 Mar 2007, P.M. Peterson 20313, R.J. Soreng & K. Romashchenko (US, USM). Puno: Chucuito, 3 km NE of Zepita on road towards Copani, 3820 m, 5 Mar 1999, P.M. Peterson 14631, N. Refulio Rodriguez & F. Salvador Perez (US, USM); 20 km E of Huacullani on road towards Desaguadero, 3880 m, 5 Mar 1999, P.M. Peterson 14645, N. Refulio Rodriguez & F. Salvador Perez (US, USM); 5 km S of Kelluyo, 3860 m, 7 Mar 1999, P.M. Peterson 14686, N. Refulio Rodriguez & F. Salvador Perez (US, USM); El Collao, 11 km E of Santa Rosa and 5 km W of Mazo Cruz, 3880 m, 2 Mar 1999, P.M. Peterson 14598, N. Refulio Rodriguez & F. Salvador Perez (US, USM); 9 km N of Conduriri and 63 km S of Ilave along the Rio Huenque, 3820 m, 3 Mar 1999, P.M. Peterson 14600, N. Refulio Rodriguez & F. Salvador Perez (US, USM); Provincia Melgar, 7 km WNW of Santa. Rosa, 14°35'54.9"S, 70°51'34.7"W, 4002 m, 23 Mar 2007, P.M. Peterson 20605, R.J. Soreng & K. Romashchenko (US, USM); SW of Juliaca ca. 8 km on Hwy 30 to Arequipa, 15°32'37.2"S, 70°12'55.9"W, 3854 m, 31 Mar 2007, P.M. Peterson 20715, R.J. Soreng, K. Romaschenko & S. Gonzalez Elizondo (US, USM); Puno, 2 km N of Laraquerion road towards Puno, 16°6'59.1"S, 70°1'59.1"W, 3940 m, 18 Apr 2004, P.M. Peterson 18327 & N. Refulio Rodriguez (US, USM); San Roman, 4 km E of Santa Lucia, 15°41'4.2"S, 70°34'8.0"W, 4030 m, 19 Apr 2004, P.M. Peterson 18332 & N. Refulio Rodriguez (US, USM); 21 km W of Santa Lucia and 5 km E of Puente Cañuma (Laguna Lagunillas), 15°40'4.1"S, 70°47'4.4"W, 4260 m, 20 Apr 2004, P.M. Peterson 18344 & N. Refulio Rodriguez (US, USM); Camjata Hacienda, Capachica Peninsula, Lake Titicaca, Tutin 975 (NY); between Juliaca and Cusco, 3880 m, 27 Nov 1923, A.S. Hitchcock 22448 (US); Hacienda Pairumani, 20 mi SW of Llave, 3900 m, 21 Jul 1946, O.P. Pearson & A. Pearson 14 (US); between Puno and Laguna Umayo, N of Puno, 3970 m, 12 Sep 1959, H.G. Barclay 9265 (US). Tacna: Cordillera Volcan Tacora, Ancara, Werderman 1138 (NY, US); Tarata, 11 km NW of Yabroco on road towards Cano, 3680 m, 16 Mar 1999, P.M. Peterson 14814, N. Refulio Rodriguez & F. Salvador Perez (US, USM).

Peru, Huacachi Estacion near Muna, summit of rocky crest, 2000 m, 20 May−1 Jun 1923, J.F. Macbride 3874 (holotype: F-534937!; isotypes: BAA-1622!, BM-000938657 [image!], G-00099373 [image!], K!, LE!, US-1256339!).

Caespitose perennials. Culms 15−40 cm tall, slender, 0.3−0.4 mm diameter just below the panicle with 6−8 nodes per culm; internodes 1−6 cm long near base, glabrous, shiny. Leaf sheaths about as long as the internodes below, glabrous; ligules 0.3−0.5 mm long, membranous, apex truncate, lacerate; blades 2−5 cm long, 1−2.2 mm wide, flat, scaberulous, apex acuminate. Panicles 3.5−6.5 (−7) cm long, 0.5−1.5 cm wide, narrow, spiciform, sometimes interrupted below; primary branches 0.5−2.5 cm long, tightly apressed to loosely ascending or spreading, not more than 45° from the culm axis. Spikelets 2.8−4.2 mm long, yellowish to light brown, erect or drooping; glumes 2.8−4 mm long, including mucos or awns, subequal, hyaline to membranous, glabrous, 1-veined, scabrous along the midvein, apex acute, unawned, mucronate or awned, the awns up to 1.3 mm long, straight or loosely flexuous; lemmas 2.8−4.2 mm long, hyaline to membranous, 3-veined, scaberulous, lower 1/3 sparsely hairy, apically awned, the awns 14−30 mm long, flexuous, callus hairy, the hairs up to 0.4 mm long; paleas about as long as the lemmas, 2-veined, glabrous, apex acuminate, often mucronate; anthers 1.3−1.6 mm long, purple. Caryopses 1.4−1.6 mm long fusiform, light brown.

Figure 9. 

A−E Muhlenbergia flexuosa Hitchc. A habit B ligule C glumes D floret E stamens and pistil. Drawn from H. Teppner 79-293 (US).

Muhlenbergia flexuosa endemic to Peru and is known from only a few collections from Huánuco, Pasco and San Martín departments (Hitchcock 1927; Tovar 1993).

Steep talus slopes, rocky trail cuts and rock outcropts with Andropogon, Acacia, Chusquea, Baccharis, Puya, Salvia, Rubus, Muhlenbergia ciliata, M. beyrichiana, Acanthaceae and Melastomataceae; 1200−2530 m.

Hitchcock (1927) suggested Muhlenbergia flexuosa was allied with M. flaviseta Scribn. and M. watsoniana Hitchc. (≡ M. scabra S. Watson), since all have short flat blades, spike-like panicles and slender flexuous awns. However, Muhlenbergia flaviseta and M. watsoniana are members of the M. subg. Clomena clade while M. flexuosa is sister to M. plumiseta Columbus−M. pereilema P.M. Peterson−M. beyrichiana clade, all of which are included in M. subg. Muhlenbergia (Fig. 1; Peterson et al. 2010b). Within Muhlenbergia, the derivation of a slender flexuous awn found in M. flexuosa has occurred in four of the five subgenera currently recognised within the genus and is only lacking in M. subg. Pseudosporobolus (Fig. 1B; Peterson et al. 2010b).