Achnatherum robustum
Achnatherum hendersonii
sleepy grass
Henderson's needlegrass, Henderson's rice grass
100-230 cm tall, 2-4.5 mm thick, mostly glabrous, often pubescent below the nodes, the pubescence antrorse or retrorse;
nodes 4-5.
10-35 cm tall, 0.3-0.9 mm thick, pubescent below the nodes, glabrous or sparsely puberulent elsewhere;
nodes 1-2.
15-30 cm long, 0.8-3.5 cm wide;
branches straight, appressed to ascending, lower branches 3-9 cm.
4-12 cm long, 2-5 cm wide, erect;
branches and pedicels straight, appressed to strongly ascending, longest branches 2-7 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, 3.5-5.5 mm long, 1-1.5 mm wide, 5-veined;
lower glumes obtuse, apices rounded to acute;
upper glumes rounded to obtuse, subequal or to 1 mm shorter than the lower glumes;
florets 3.5-4.5 mm long, 1-1.5 mm wide, fusiform, laterally compressed;
calluses 0.3-0.5 mm, blunt;
lemmas coriaceous, glabrous, shiny, apical lobes about 0.2 mm long, thick;
awns 6-10 mm, readily deciduous, not geniculate, scabrous;
paleas about 3 mm, from3/4 as long as to equaling the lemmas, indurate, glabrous, apices rounded, flat;
anthers about 2.5 mm, dehiscent, penicillate.
5-6 mm.
2.5-4 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 completely or mostly glabrous, margins sometimes ciliate distally;
collars glabrous;
ligules 0.4-1 mm, hyaline, glabrous or pubescent, rounded;
blades tightly folded or convolute, to 1 mm wide or thick, abaxial surfaces scabrous, adaxial surfaces pubescent.
= 64.
= 34.
Achnatherum robustum
Achnatherum hendersonii
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 hendersonii grows in dry, rocky, shallow soil, in sagebrush or ponderosa pine associations. It is known from only three counties: Yakima and Kittitas counties, Washington, and Crook County, Oregon. Maze (1981) noted that, at one site, A. hendersonii was restricted to areas subject to frost heaving, although under cultivation, it can grow without such disturbance. He hypothesized that its survival in such sites is attributable to a competitive advantage gained by the structure of its root system. Unlike Poa secunda, which grew in the surrounding, undisturbed areas, the outer cortex and epidermis of the roots of A. hendersonii form a sheath around the stele and inner cortex. When the roots are pulled, this sheath slips and breaks but the internal structures remain intact. In Poa secunda, the outer part of the root is attached to the central core and, when the roots are pulled, they break. Achnatherum hendersonii also differs from P. secunda in having relatively few (9-12), evenly distributed roots that extend to 30 cm.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
KS Wildflowers
WildflowerSearch
iNaturalist
USDA Plants Database
OR
WA
Flora NW
PNW Herbaria
