Achnatherum richardsonii
Achnatherum hendersonii
Richardson needlegrass, Richardson's needlegrass, Richardson's rice grass, spreading needlegrass
Henderson's needlegrass, Henderson's rice grass
30-100 cm tall, 1-1.5 mm thick, glabrous;
nodes usually 3.
10-35 cm tall, 0.3-0.9 mm thick, pubescent below the nodes, glabrous or sparsely puberulent elsewhere;
nodes 1-2.
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.
4-12 cm long, 2-5 cm wide, erect;
branches and pedicels straight, appressed to strongly ascending, longest branches 2-7 cm.
pendulous.
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.
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.
2.5-4 mm.
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 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.
= 44.
= 34.
Achnatherum richardsonii
Achnatherum hendersonii
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 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.)
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