Muhlenbergia uniseta (Lag.) Columbus, Aliso 28: 66. 2010.

Peterson, Paul M., Herrera Arrieta, Yolanda, Lobo Cabezas, Silvia & Romaschenko, Konstantin, 2023, Taxonomic revision of Muhlenbergia (Poaceae, Chloridoideae, Cynodonteae, Muhlenbergiinae) in Central America: phylogeny and classification, PhytoKeys 230, pp. 1-106 : 1

34. Muhlenbergia uniseta (Lag.) Columbus, Aliso 28: 66. 2010.

Fig. 20F, G

Hymenothecium unisetum Lag., Gen. Sp. Pl. 4. 1816. Type: México, cultivated from seed at MA, D. Sessé & Mociño s.n. (holotype: MA). ≡ Aegopogon geminiflorus var. unisetus (Lag.) E. Fourn., Mexic. Pl. 2: 71. 1886. Basionym:

= Lamarckia tenella DC., Cat. Pl. Horti Monsp. 120. 1813. Type: cult. hort. Monsp., De Candolle s.n. (lectotype, designated here: US-75926! ex MPU; isolectotype: US-75925! ex MPU). ≡ Hymenothecium tenellum (DC.) Lag., Gen. Sp. Pl. 4. 1816. ≡ Aegopogon tenellus (DC.) Trin., Gram. Unifl. Sesquifl. 164. 1824.

= Schellingia tenera Steud., Flora 33: 232. 1850. Type: México, Oaxaca, Cordillera, 1840, H. Galeotti 5750 (lectotype, designated here: P-00745714 [image!]; isolectotypes: P-00745713 [image!], P-00745715 [image!], W-18890117307 [image!], W-0001035 [image!]).

Description.

Slender often sprawling, caespitose annuals. Culms (2-)6-30 cm tall, 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 sparsely pilose; ligules 0.6-1.5 mm long, apex mostly truncate, lacerate; blades 1.5-6 cm long, 0.5-1.5(-1.7) mm wide, flat, scaberulent and pubescent above, smooth beneath. Panicles 2-6 cm long, 0.5-1.2 cm wide, open, loosely-flowered with racemose branches; primary branches 3-5 mm long, excluding the awns, one per node; one short-pedicelled spikelet (perfect) with pedicels 0.2-0.6 mm long and the other two spikelets (staminate or sterile) short-pedicelled, the pedicels about 0.7-1.5 mm long. Spikelets 1.5-3.2 mm long, often greenish or purplish; glumes (1-)1.3-2 mm long, oblong and wider distally, apex deeply notched, entire or mucronate, the mucro 0.2-1 mm long, lobes obtuse or rounded; lemmas 2.5-3.2 mm long, 3-awned, the central awns 3-8(-11) mm long, lateral awns usually mucronate or awned up to 2 mm long or missing; paleas 2.2-3 mm long, puberulent, apex 2-mucronate, the mucros less than 0.8 mm long; anthers 0.5-0.8 mm long, yellowish. Caryopses 1.1-1.3 mm long, obovoid, light brownish. 2 n = 20, 60.

Distribution.

Muhlenbergia uniseta ranges from southern Arizona throughout most of México and Central America (Belize, Costa Rica, El Salvador, Guatemala, Honduras, México, and Panama) [ Pohl 1994a; Peterson et al. 2001].

Ecology.

Muhlenbergia uniseta grows on moist slopes, cliffs, barrancas, canyons, roadsides, and along or near springs usually in shaded areas associated with Pinus and Quercus ; 1300-2860 m.

Comments.

Muhlenbergia uniseta can be separated morphologically from M. cenchroides in having glumes with obtuse or rounded lobes (acute in M. cenchroides ) that are entire or mucronate (awned 2-4 mm long in M. cenchroides ) and by being annual (versus perennial).

Muhlenbergia uniseta is a member of M. subg. Muhlenbergia and forms a clade with M. cenchroides and M. bryophilus (Fig. 1 ; Peterson et al. 2021).

Specimens examined.

Costa Rica. Heredia: San Isidro, Concepción, Calle Leones, E. Alfaro 4724 (INB). San José: Dota, R.F. Los Santos. Cuenca del Pirris-Damas , Rio Blanco , cabeceras Quebrada Vueltas, J.F. Morales 7088 (MO); vicinity of Santa Maria de Dota , P.C. Standley 41720 (US); Aserrí, Cuenca del Pirris-Damas , Cerros Caraigres, Falda S, Quebrada Concha, en el camino viejo a Bijagual, J.F. Morales 5914 (MO, INB); Aserri, Z.P. Cerros Escazú, Cuenca del Tarcoles , bosques primarios y secundarios en la cima del Cerro Daser (Alto Hierbabuena), J.F. Morales 6707 (MO,INB); Acosta, Alto Reflis, Falda NE, Fila de Cal , J.F. Morales 7486 (CR, INB); Desamparados, Tablazo, J.A. Echeverría 1210 (CR); Entre San Isidro y División, s.c 3855 (CR); Cord. Talamanca, 14 km S of Division along the Interamericana Hwy., roadside through oak forest, R.W. Pohl & G. Davidse 11615 (US). El Salvador. La libertad: E. Montalvo et al. 6425 (LAGU). Santa Ana: O. Rohweder 2394 (MO). Usulután: J. Menjívar et al. 3591 (LAGU, MHES, MO); G. Cerén et al. 3276 (MHES, MO). Guatemala. Guatemala: Volcan de Pacaya , above Las Calderas, P. C. Standley 58340 (US); Volcan de Acatenango , J. & M. Véliz 93.3425 (MEXU). Sacatepéquez: Ciudad Vieja, H. Bethancourt & M. Véliz 94.4181 (MEXU, MO). Sololá: near Sololá, A. Gentry 6504 (MO); slopes of Volcan de Agua , south of Santa Maria de Jesus , P.C. Standley 59361 (US). Honduras. Francisco Morazán: El Zamorano, North side of Cerro Uyuca, near the farmhouse, R. W. Pohl & M. Gabel 13413 (CR); On open slopes near Hoya Grande, L.O. Williams & A. Molina 10994 (US); Open slopes in cloud forest area in mountains above San Juancito, L.O. Williams & A. Molina 13366 (US); Santa Lucía, camino entre la montañita y Santa Lucía, J.L. Linares & J. Alana 1901 (MEXU); Escuela Agrícola Panamericana, Faldas de La Montañita, A. Molina R. 1612A (US). Mexico. Chiapas: Huixtlán: 10 km E of Huistan, D.E. Breedlove & G. Davidse 55169 (MEXU); D.E. Breedlove & G. Davidse 53853 (MO). Larráinzar: NE of Bochil, D.E. Breedlove 29276 (MEXU). San Cristóbal de las Casas: 16 km al NW de San Cristobal de las Casas, sobre el camino a Tenejapa, E. Cabrera & H. de Cabrera 5733 (MEXU). Zinacantan: hwy 190 between paraajes of Nachic and Navenshauk, D.E. Breedlove 7304 (US). Panama. Chiriquí: Large old lava flow ca. 3 km NE of El Hato del Volcán at base of Volcán de Chiriquí ( Barú), 1-3 km E of highway, G. Davidse & W.G. D’Arcy 10386 (MO) .

Figures

Figure 1. A, B Bayesian tree inferred from combined plastid (ndhA intron, rps 16 - trnK, rps 16 intron, rps 3, and rpl 32 - trnL) and ITS sequences. Thick branches indicate posterior probabilities of 0.95 - 1; species in bold occur in Central America; Scale bar: 2 %.

Figure 20. A-E Muhlenbergia robusta (E. Fourn.) Hitchc. A habit B ligule C glumes D floret E stamens, pistil, and lodicules F, G Muhlenbergia uniseta (Lag.) Columbus F habit G primary inflorescence branch with three spikelets. A-E drawn from P. M. Peterson & C. R. Annable 6131 (US) F, G drawn from F. W. Gould 10391 (US- 3000113).