Achnatherum robustum
Achnatherum swallenii
sleepy grass
Swallen'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.
15-25 cm tall, 0.5-1 mm thick, glabrous;
nodes 2-3.
15-30 cm long, 0.8-3.5 cm wide;
branches straight, appressed to ascending, lower branches 3-9 cm.
3-6.5 cm long, 0.3-0.7 cm wide;
branches appressed, lower branches 1-5 cm, with 1-5 spikelets.
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, 4-5.5 mm, not saccate, apices narrowly acute to acuminate, midveins often prolonged into an awnlike tip;
lower glumes 0.6-1 mm wide, apices narrowly acute;
florets 2.5-3.5 mm long, 0.6-0.8 mm thick, fusiform, terete;
calluses 0.1-0.2 mm, blunt;
lemmas evenly hairy, hairs 0.3-0.5 mm, all similar in length, apical lobes 0.3-0.5 mm, thickly membranous;
awns 5-6 mm, once-geniculate, readily deciduous, basal segment scabridulous;
paleas 2.2-2.5 mm, slightly shorter than the lemmas;
anthers 1.5-2 mm, dehiscent, not penicillate.
5-6 mm.
2-3 mm, ovoid.
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 mostly glabrous, pubescent at the base, throats glabrous;
collars, including the sides, glabrous;
basal ligules 0.2-0.3 mm, obtuse to rounded, glabrous;
upper ligules to 0.5 mm, rounded to broadly acute;
blades 0.4-0.7 mm wide, arcuate, abaxial surfaces smooth or scabridulous, adaxial surfaces with hairs shorter than 0.5 mm.
= 64.
= 34.
Achnatherum robustum
Achnatherum swallenii
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 swallenii grows on open, rocky sites, frequently with low sagebrush, in Idaho and western Wyoming, at 1500-2200 m. It is a dominant species in parts of eastern Idaho, although it is poorly represented in collections.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
KS Wildflowers
WildflowerSearch
iNaturalist
USDA Plants Database
PNW Herbaria
