Achnatherum robustum
Achnatherum coronatum
sleepy grass
crested needlegrass, giant ricegrass
100-230 cm tall, 2-4.5 mm thick, mostly glabrous, often pubescent below the nodes, the pubescence antrorse or retrorse;
nodes 4-5.
55-210 cm tall, 3-6 mm thick, internodes usually glabrous, lower internodes sometimes puberulent;
nodes 1-2, glabrous.
15-30 cm long, 0.8-3.5 cm wide;
branches straight, appressed to ascending, lower branches 3-9 cm.
15-60 cm long, 2-4 cm wide;
branches widely spreading to ascending, longest branches 4-13 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.
lanceolate, glabrous, tapering to awnlike apices;
lower glumes 16-21 mm long, 1-1.3 mm wide, midveins scabrous;
upper glumes 11-18 mm;
florets 6.5-10 mm long, about 1 mm thick, fusiform, terete;
calluses 0.5-2 mm, blunt to acute;
lemmas densely hairy, hairs at midlength 1.5-4 mm, apical hairs 2-5 mm;
awns 25-45 mm, persistent, twice-geniculate, all segments scabrous, terminal segment straight;
paleas 3.5-5.5 mm, 3/5 – 9/10 as long as the lemmas, sparsely hairy between the veins, apices flat, rounded;
anthers 3-4 mm, dehiscent, not penicillate.
5-6 mm.
5-7 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 mostly glabrous, often puberulent on the lower portion, flat, ribbonlike with age, margins hairy distally, hairs 1-2.5 mm;
collars mostly glabrous;
ligules 0.4-1.6(3) mm, truncate to slightly rounded, abaxial surfaces pubescent, ciliate, cilia about 0.5 mm;
blades usually flat, 2.5-7 mm wide, both surfaces scabrous.
= 64.
= 40.
Achnatherum robustum
Achnatherum coronatum
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 coronatum grows on gravel and on rocky slopes, mostly in chaparral associations of the Coast Range from Monterey County, California, to Baja California, Mexico. It is similar in size to A. diegoense, but differs in its mostly glabrous internodes and longer paleas. It differs from A. parishii, an inland species, in its twice-geniculate awns, more robust habit, and more sparsely pubescent paleas. Occasional plants combine the characteristics of both species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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