Achnatherum robustum
Achnatherum richardsonii
sleepy grass
Richardson needlegrass, Richardson's needlegrass, Richardson's rice grass, spreading 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.
30-100 cm tall, 1-1.5 mm thick, glabrous;
nodes usually 3.
15-30 cm long, 0.8-3.5 cm wide;
branches straight, appressed to ascending, lower branches 3-9 cm.
7-25 cm long, 7-15 cm wide;
branches divergent, flexuous, longest branches 7-10 cm, with the spikelets confined to the distal 1/4.
appressed to the branches.
pendulous.
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.
7.5-11 mm long, 0.9-1.2 mm wide;
upper glumes 2-3 mm shorter;
florets 5-6 mm long, 0.6-0.9 mm thick, fusiform, terete;
calluses 0.4-0.7 mm, blunt;
lemmas evenly hairy on the lower portion, often glabrate distally, body and apical hairs 0.2-0.5 mm, apical lobes not or scarcely developed, to 0.1 mm;
awns 15-25 mm, persistent, twice-geniculate, first 2 segments strigulose, hairs about 0.1 mm, terminal segment straight;
paleas 2.2-3.6 mm, 1/2 - 3/5 as long as the lemmas, pubescent, hairs not exceeding the apices, apices rounded;
anthers 2.5-3 mm, dehiscent, penicillate, hairs 0.1-0.5 mm.
5-6 mm.
3-4 mm, fusiform.
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, margins ciliolate;
collars glabrous, without tufts of hair on the sides;
ligules 0.1-0.5 mm, truncate, ciliolate;
blades 0.8-3 mm wide, convolute when dry, abaxial surfaces scabridulous, adaxial surfaces glabrous.
= 64.
= 44.
Achnatherum robustum
Achnatherum richardsonii
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 richardsonii grows in open woodlands and grasslands,often on sand or gravel, from the Yukon Territory to Washington and Manitoba, and south in the Rocky Mountains through Montana and Wyoming to western South Dakota and northern Colorado. Its elevation range is 1000-3100 m. It is readily recognized by its combination of flexuous panicle branches, drooping spikelets, and straight distal awn segments. Scagel and Maze (1984) concluded that putative hybrids between A. richardsonii and A. nelsonii subsp. dorei were merely large plants of subsp. dorei that varied in the direction of A. richardsonii.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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