Achnatherum aridum

(M.E. Jones) Barkworth
Common names: Mormon needlegrass
Synonyms: Stipa arida unknown
Treatment appears in FNA Volume 24. Treatment on page 131.
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Illustrator: Cindy Roché
Plants cespitose, not rhizomatous. Culms 35-85 cm tall, 0.9-2.5 mm thick, usually glabrous and smooth, sometimes scabridulous or puberulent; nodes 2-3. Basal sheaths glabrous, upper sheath margins hyaline distally; collars of the basal sheaths occasionally with a small tuft of 0.8 mm hair on the sides, collars of the upper leaves glabrous, scabridulous, or sparsely puberulent; ligules 0.2-1.5 mm, truncate to rounded, erose, sometimes ciliate, cilia about 0.05 mm; blades 0.9-3 mm wide, abaxial surfaces smooth or scabridulous, glabrous, adaxial surfaces hirtellous, hairs to 0.5 mm. Panicles 5-17 cm long, 1-1.5 cm wide, contracted, bases often enclosed at anthesis; branches appressed or strongly ascending, straight, lower branches 1.5-4 cm. Lower glumes 8-15 mm long, 0.6-0.8 mm wide; upper glumes 1-5 mm shorter; florets 4-6.5 mm long, 0.6-1.1 mm thick, fusiform, terete; calluses 0.2-1 mm, sharp; lemmas evenly hairy on the lower portion, hairs 0.2-0.5 mm, the distal 1/5 – 1/4 often glabrous, apical hairs absent or fewer than 5, to 1.5 mm; awns 40-80 mm, persistent, obscurely once-geniculate, scabridulous, terminal segment flexuous; paleas 2-3.2 mm, 1/2 - 3/4 as long as the lemmas, pubescent, hairs exceeding the apices, apices rounded, flat; anthers 2-3.5 mm, dehiscent, not penicillate. 2n = unknown.


Colo., N.Mex., Tex., Utah, Calif., Ariz., Nev.


Achnatherum aridum grows on rocky outcrops, in shrub-steppe and pinyon-juniper associations, from southeastern California to Colorado and New Mexico, at 1200-2000 m. It has also been reported from Texas, but no specimens documenting these reports have been located. It has not been found in Mexico.



Lower Taxa

No lower taxa listed.