Achnatherum richardsonii |
Achnatherum thurberianum |
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Richardson needlegrass, Richardson's needlegrass, Richardson's rice grass, spreading needlegrass |
Thurber's needlegrass, Thurber's rice grass |
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Habit | Plants tightly cespitose, not rhizomatous. | Plants cespitose, not rhizomatous. |
Culms | 30-100 cm tall, 1-1.5 mm thick, glabrous; nodes usually 3. |
30-75 cm tall, 0.5-1.7 mm thick, internodes pubescent or glabrous, pubescence more common on the lower internodes, particularly just below the nodes; nodes 2-3, lower nodes retrorsely pubescent, upper nodes glabrous or pubescent. |
Panicles | 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. |
7-15 cm long, 0.5-2.5 cm wide, often included in the upper leaf sheaths at the start of anthesis; branches 1.5-6 cm, appressed to strongly ascending, with 1-6 spikelets. |
Spikelets | pendulous. |
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Glumes | often purplish; lower glumes 10-15 mm long, 1.2-2 mm wide; upper glumes to 2 mm shorter; florets 6-9 mm long, 0.7-1.2 mm thick, fusiform, terete; calluses 0.9-1.5 mm, sharp; lemmas coriaceous, evenly pubescent or the back glabrate distally, hairs 0.5-0.8 mm, apices lobed on 1 margin, lobe about 0.1 mm long, thick, apical lemma hairs 0.5-0.8 mm; awns 32-56 mm, twice-geniculate, first 2 segments pilose, hairs 0.8-2 mm, terminal segment glabrous, often scabrous; paleas 4.6-6.1 mm, 3/4 - 9/10 as long as the lemmas, sparsely pubescent towards the base; anthers 2.5-3.5 mm, dehiscent, not penicillate. |
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Lower glumes | 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. |
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Caryopses | 3-4 mm, fusiform. |
5-7 mm, fusiform. |
Basal | 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 glabrous, usually smooth, brown or gray-brown; collars glabrous, without tufts of hair at the sides; basal ligules 1.5-6 mm, hyaline, rounded to acute, lacerate; upper ligules to 8 mm, hyaline, acute, glabrous; blades 0.5-2 mm wide, convolute, abaxial surfaces scabrous, adaxial surfaces scabrous or hairy, hairs about 0.3 mm. |
2n | = 44. |
=34. |
Achnatherum richardsonii |
Achnatherum thurberianum |
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Distribution |
AK; CO; ID; MT; SD; WA; WY; AB; BC; MB; SK; YT
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CA; CO; ID; MT; NV; OR; UT; WA; WY
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Discussion | 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 thurberianum grows in canyons and foothills, primarily in sagebrush desert and juniper woodland associations, from Washington to southern Idaho and southwestern Montana and from California to Utah, at 900-3000 m. Its long ligules and pilose awns make it one of the easier North American species of Achnatherum to identify. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 24, p. 133. | FNA vol. 24, p. 125. |
Parent taxa | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum |
Sibling taxa | ||
Synonyms | Stipa richardsonii | Stipa thurberiana |
Name authority | (Link) Barkworth | (Piper) Barkworth |
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