Plants cespitose, shortly rhi-zomatous, bases knotty. Culms 50-100 cm tall, 0.8-1.5 mm thick, glabrous; nodes 2-3. Basal sheaths mostly glabrous, ciliate on the margins; collars glabrous on the back, usually with tufts of hair on the sides, hairs about 0.8 mm; basal ligules 0.8-1.6 mm, membranous, glabrous, rounded to acute; upper ligules to 4.5 mm, acute; blades 0.7-3.5 mm wide, abaxial surfaces smooth to scabridulous, adaxial surfaces prominently ribbed, scabridulous or sparsely to densely pubescent, hairs about 0.1 mm. Panicles 20-55 cm long, 3-8 cm wide, open, often enclosed to midlength at anthesis; lower branches 5-8 cm, ascending to divergent, flexuous. Lower glumes 5-12 mm long, 0.5-0.7 mm wide, 3-5-veined; upper glumes 1-4 mm shorter, 3-veined; florets 4-7.5 mm long, 0.5-0.9 mm thick, fusiform, terete; calluses 1-2 mm, sharp; lemmas evenly hairy, hairs 0.4-0.8 mm throughout, apical lobes not present; awns 35-70 mm, persistent, twice-geniculate, first 2 segments scabrous, terminal segment flexuous; paleas 1-2 mm, 1/3-1/2 as long as the lemmas, sparsely to moderately pubescent, apices rounded, flat; anthers 3-3.5 mm, dehiscent, a few penicillate, hairs about 0.3 mm. Caryopses about 4 mm, fusiform. 2n = 44, 46.
Achnatherum eminens grows on dry, rocky slopes and valleys in the mountains of the southwestern United States, primarily in desert scrub, at 600-2600 m. Its range extends into Mexico. It is easy to recognize because of its open panicle, flexuous branches, and flexuous awns. It is superficially similar to Nassella cernua, but differs in its longer, glabrous ligules, not or weakly overlapping lemma margins, pubescent paleas, and geographic distribution.
FNA 2007, Gould 1980
Common Name: southwestern needlegrass Duration: Perennial Nativity: Native Lifeform: Graminoid General: Perennial plants tufted, shortly rhizomatous, knotty bases; stems 50-100 cm tall, strictly erect. Vegetative: Sheaths glabrous, ciliate on margins, collars with tufts of hair on the sides, hairs about 1 mm; basal ligules 0.5-1.5 mm, membranous, glabrous, rounded to acute, upper ligules to 4.5 mm, acute; blades 0.5-3.5 mm wide, flat to involute, lower surfaces smo Inflorescence: Panicles 20-55 cm long, 3-8 cm wide, open, enclosed to midlength at anthesis, flexuous; lower branches 5-8 cm, ascending to divergent, flexuous; lower glumes 5-12 mm long, 3-5 veined; upper glumes 1-4 mm shorter, 3-veined; florets 4-7.5 mm long, 0.5-1 mm thick, terete; lemmas evenly hairy, hairs minute, apical lobes not present; awns 35-70 mm, persistent, twice-geniculate, first 2 segments scabrous, terminal segment flexuous; paleas 1-2 mm, half to third as long as lemmas, moderately pubescent, apices rounded to flat. Ecology: Found on dry slopes, often on rocky soils from 2,000-8,500 ft (610-2591 m); flowers August-October. Distribution: se AZ, s NM, sw TX; south to c MEX. Notes: Distinguished by an open panicle, single floret spikelets (single seeded spikelets) with long awns 30-70 mm which are often bent or corkscrewed in two turns (twice geniculate). Look for plants often growing from beneath other plants and sticking up above shrubs and other vegetation to over a meter tall with large, open panicles with wispy, long awns. Ethnobotany: Unknown, but other species in the genera were eaten. Etymology: Achnatherum comes from the Greek achne, for chaff or glume and ather for stalk or barb, so stalked or barbed lemma, while eminens means projecting or eminent. Synonyms: Stipa eminens Editor: SBuckley 2010, FSCoburn 2014