Achnatherum robustum
Achnatherum webberi
sleepy grass
Webber needlegrass, Webber's 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.
12-35 cm tall, 0.4-0.7 mm thick, smooth or antrorsely scabridulous;
nodes 2-3.
15-30 cm long, 0.8-3.5 cm wide;
branches straight, appressed to ascending, lower branches 3-9 cm.
2.5-7 cm long, 0.5-2 cm wide, contracted;
branches appressed, longest branches 1-2 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.
subequal, 6-10 mm long, 0.6-0.9 mm wide, lanceolate, not saccate;
florets 4.5-6 mm long, 0.7-1 mm thick, fusiform, terete;
calluses 0.3-0.8 mm, blunt;
lemmas evenly and densely pilose, hairs 2.5-3.5 mm, apical lobes 0.6-1.9 mm, membranous;
awns 4-11 mm, readily deciduous, straight to once-geniculate, scabrous;
paleas 4-5.6 mm, from as long as to slightly longer than the lemmas;
anthers 1.6-2 mm, dehiscent, not penicillate.
5-6 mm.
3.5-4.5 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, smooth or scabridulous;
collars glabrous, without tufts ' of hair on the sides;
basal ligules 0.1-1 mm, truncate to rounded;
upper ligules 1-2 mm, acute;
blades 0.5-1.5 mm wide when flat, usually folded to involute and about 0.5 mm in diameter, stiff, abaxial surfaces smooth or scabrous, adaxial surfaces scabrous.
= 64.
= 32.
Achnatherum robustum
Achnatherum webberi
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 webberi grows in dry, open flats and on rocky slopes, often with sagebrush, at 1500-2500 m. It grows at scattered locations from Oregon and Idaho to California and Nevada. It differs from A. hymenoides in its cylindrical floret and non-saccate glumes, and from A. pinetorum and A. parishii subsp. parishii in its shorter, deciduous awns. It also has narrower blades than A. parishii subsp. depauperatum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
KS Wildflowers
WildflowerSearch
iNaturalist
USDA Plants Database
CA
OR
Flora NW
PNW Herbaria
