Plants annual. Culms 10-38 cm, erect or spreading; internodes mostly glabrous, smooth or scabridulous, scabrous or strigulose below the nodes. Sheaths often longer than the internodes, scabridulous, margins hyaline; ligules 1-3 mm, hyaline, obtuse, irregularly toothed to lacerate, with lateral lobes; blades 1-10 cm long, 0.4-2 mm wide, flat, scabrous abaxially, strigulose adaxially, margins and midveins thickened basally, whitish. Panicles 10-24 cm long, 3.5-11 cm wide, diffuse; primary branches 2.2-6.2 cm long, about 0.1 mm thick, diverging 80-100° from the rachises, straight; pedicels 6-10 mm long, about 0.02 mm thick, delicate; disarticulation above the glumes. Spikelets 1-1.2 mm, appressed to slightly divergent. Glumes equal to subequal, 0.5-1 mm, glabrous throughout or obscurely puberulent, hairs about 0.06 mm, 1-veined, obtuse or subacute; lemmas 1-1.2 mm, oblong-elliptic, purplish to light brownish, not mottled, glabrous or densely appressed-puberulent on the margins and midveins, apices obtuse, unawned; paleas 0.9-1.2 mm, oblong-elliptic; anthers 0.3-0.5 mm, purplish. Caryopses 0.7-0.9 mm, elliptic, reddish-brown. 2n = 20.
Muhlenbergia fragilis grows on rocky talus slopes, cliffs, canyon walls, road cuts, and sandy slopes, often over calcareous parent materials, at elevations of 480-2200 m. It is usually found in oak-grama savannahs, thorn scrub forests, oak-yellow pine forests, and pinyon-juniper woodlands. Its range extends from the southwestern United States to southern Mexico.
Populations may have individual plants with completely glabrous lemmas or may consist entirely of such plants. This morphological variation is not correlated with any distributional or habitat characteristics.
FNA 2003, Gould 1980
Common Name: delicate muhly Duration: Annual Nativity: Native Lifeform: Graminoid General: Delicate annual grass, stems much branched below, erect or spreading, 10-30 cm, strigose below the nodes. Vegetative: Blades to 5 cm long, 1-2 mm wide, flat or folded, scabrous, with prominent, white, thickened midnerve and margins; sheaths longer than internodes, scaberulous, with hyaline margins; decurrent margins of sheath extending up as prolongations 1-3 mm long; li Inflorescence: Panicles often purple, very diffuse and open and readily breaking off at maturing; numerous usually solitary slender branches becoming stiffly spreading or even reflexed; branchlets divergent; spikelets tiny, about 1 mm long; glumes obtuse to subacute, glabrous, 0.5-1 mm long; lemma obtuse, glabrous or densely pubescent on keel and margins; palea equaling lemma in length, caryopsis elliptic, less than 1 mm, reddish brown. Ecology: Rocky talus slopes, cliffs, canyon walls, road cuts, and sandy slopes, often over calcareous parent materials, from 2,500-6,500 ft (762-1981 m); flowers August-October. Distribution: s CA, s NV, AZ, NM, w TX; south to s MEX. Notes: Muhlenbergia is a large and diverse genus primarily distinguished by having single-flowered spikelets with unequal glumes. This species is a small, delicate annual muhly with open, diffuse inflorescences and is told apart from other annual muhlys by its being awnless and having hairless glumes. It can form dense stands resembling fog on the ground after summer rains. Ethnobotany: Unknown Etymology: Muhlenbergia is named for Gotthilf Heinrich Ernst Muhlenberg (1753-1815) a clergyman and botanist from Pennsylvania; fragilis means delicate or fragile. Synonyms: None Editor: SBuckley 2010, FSCoburn 2014, AHazelton 2015