Achnatherum robustum
Achnatherum aridum
sleepy grass
arid needlegrass, Mormon needlegrass
100-230 cm tall, 2-4.5 mm thick, mostly glabrous, often pubescent below the nodes, the pubescence antrorse or retrorse;
nodes 4-5.
35-85 cm tall, 0.9-2.5 mm thick, usually glabrous and smooth, sometimes scabridulous or puberulent;
nodes 2-3.
15-30 cm long, 0.8-3.5 cm wide;
branches straight, appressed to ascending, lower branches 3-9 cm.
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.
appressed to the branches.
subequal, 9-11.5 mm long, 1-1.4 mm wide;
florets 5.9-8.5 mm long, 0.9-1.2 mm thick, fusiform, terete;
calluses 0.3-1 mm, blunt;
lemmas evenly hairy, hairs at midlength 0.3-0.8 mm, apical hairs to 1.5 mm;
awns 20-32 mm, persistent, twice-geniculate, scabridulous to scabrous, scabrules to about 0.1 mm, longest on the middle segment, terminal segment straight;
paleas 3.7-5.6 mm, 2/3 - 3/4 as long as the lemmas, hairy, hairs about 0.5 mm, not exceeding the apices, veins terminating below the apices, apices rounded;
anthers 4-5 mm, dehiscent, penicillate.
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.
5-6 mm.
sheaths mostly glabrous, margins usually ciliate distaily;
collars hairy, those of the flag leaves densely hairy, hairs 0.5-2 mm, sides glabrous;
basal ligules 1-2 mm;
upper ligules to 4 mm, truncate, rounded, or obtuse, glabrous;
blades 6-10 mm wide, glabrous, abaxial surfaces smooth, adaxial surfaces prominently ribbed, ribs scabrous.
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.
= 64.
= unknown.
Achnatherum robustum
Achnatherum aridum
Achnatherum robustum grows on dry plains and hills, in open woods and forest clearings, and along roadsides, from Wyoming through Colorado to Arizona, New Mexico, and northern Mexico. Records from Kansas represent recent introductions; it is not clear whether the species has persisted there. Achnatherum robustum is sometimes confused with A. nelsonii subsp. dorei and Nassella viridula; it differs from both in the densely hairy collars of its flag leaves. Although not widely available, it has potential as an ornamental grass, particularly in arid regions with cold winters.
The English-language name refers to the effect some samples, particularly those from the Sacramento and Sierra Blanca mountains, New Mexico, have on livestock, especially horses and cattle. "Mildly poisoned animals are dejected, inactive, and withdrawn; severely poisoned animals lie on their sides in a profound slumber" (Cheeke and Shull 1985). The active ingredient is diacetone alcohol (Epstein et al 1964).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
KS Wildflowers
WildflowerSearch
iNaturalist
USDA Plants Database
CA
