Achnatherum richardsonii
Achnatherum latiglume
Richardson needlegrass, Richardson's needlegrass, Richardson's rice grass, spreading needlegrass
Sierra needlegrass, wide-glumed needlegrass
30-100 cm tall, 1-1.5 mm thick, glabrous;
nodes usually 3.
50-110 cm tall, 0.7-1.2 mm thick, lower internodes retrorsely pilose, upper internodes glabrous;
nodes 2-4.
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.
15-30 cm long, 0.8-2 cm wide;
branches appressed to strongly ascending, longest branches 2.5-6.5 cm.
pendulous.
subequal, 12-15 mm long, 1.3-1.9 mm wide, 3-veined;
florets 8-9 mm long, 0.9-1.4 mm thick, fusiform, terete;
calluses 0.7-1 mm, blunt to sharp;
lemmas evenly hairy, hairs 0.5-1.5 mm at midlength, apical hairs 1-2 mm, apical lobes to 1 mm, membranous;
awns 33-45 mm, persistent, twice-geniculate, first 2 segments pilose, with hairs 0.5-2 mm, terminal segment mostly scabrous, straight;
paleas 4-5 mm, 3/5 – 4/5 as long as the lemmas, pubescent;
anthers not seen.
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.
3-4 mm, fusiform.
not seen.
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.
sheaths usually retrorsely pubescent, brown to gray-brown, flat when mature;
collars usually glabrous, sometimes with a few hairs at the sides;
basal ligules 0.2-2.5 mm, truncate to rounded;
upper ligules 1.2-3 mm, rounded to acute, ciliate;
blades 0.7-3 mm wide, straight to lax, abaxial surfaces smooth, glabrous, adaxial surfaces pubescent, scabrous.
= 44.
= 70.
Achnatherum richardsonii
Achnatherum latiglume
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.)
Achnatherum latiglume usually grows on dry slopes in yellow pine forests of southern California. Pohl (1954) demonstrated that it is an alloploid derivative of A. nelsonii and A. lemmonii. He reported being told that it was a fairly common species in the Yosemite Valley, and suggested that the isolated occurrences in Riverside and Fresno counties might represent separate origins of the species.
Achnatherum latiglume resembles A. nevadense and A. occidental, but the latter two species have sharper calluses, and their paleas tend to be thinner and somewhat shorter relative to the lemmas than those of A. latiglume.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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