Achnatherum nelsonii |
Achnatherum hymenoides |
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Columbia needle grass, Nelson achnatherum, Nelson's needlegrass |
Indian rice grass, sand needlegrass, sand ricegrass |
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Habit | Plants cespitose, not rhizomatous. | Plants tightly cespitose, not rhizomatous. | ||||
Culms | 40-175 cm tall, 0.7-2.4 mm thick, lower cauline internodes usually glabrous, sometimes slightly pubescent below the lower nodes; nodes 2-5. |
25-70 cm tall, 0.7-1.3 mm thick, glabrous or partly scabridulous; nodes 3-4. |
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Sheaths | glabrous or scabridulous, sometimes puberulent on the distal margins, hairs to 0.8 mm; collars glabrous, sometimes with tufts of hair on the sides, hairs to 1 mm; basal ligules 1.5-4 mm, hyaline, glabrous, acute; upper ligules to 2 mm; blades usually convolute, 0.1-1 mm in diameter, abaxial surfaces smooth or scabridulous, adaxial surfaces pubescent. |
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Panicles | 9-36 cm long, 0.8-2 cm wide; branches ascending to appressed, straight. |
9-20 cm long, 8-14 cm wide; branches ascending to strongly divergent, longest branches 3-15 cm; pedicels paired, conspicuously divaricate, shorter pedicels in each pair usually at least 1/2 as long as the longer pedicels. |
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Spikelets | appressed to the branches. |
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Glumes | 6-12.5 mm long, 0.7-1.1 mm wide; lower glumes exceeding the upper glumes by 0.2-0.8 mm; florets 4.5-7 mm long, 0.6-0.9 mm thick, fusiform; calluses 0.2-1 mm, blunt to sharp, dorsal boundary of the glabrous tip with the callus hairs almost straight to acute; lemmas evenly hairy, hairs at midlength 0.5-1 mm, hairs at the apices to 2 mm, erect to ascending, apical lobes 0.1-0.4 mm, membranous, flexible; awns 19-45 mm, persistent, twice-geniculate, first 2 segments scabrous or with hairs shorter than 0.5 mm, terminal segment straight; paleas 2-4 mm, 1/3 – 2/3 as long as the lemmas, pubescent, hairs usually not exceeding the apices, veins terminating before the apices, apices rounded; anthers 2-3.5 mm, dehiscent, not penicillate. |
subequal, 5-9 mm long, 0.8-2 mm wide, saccate below, puberulent, hairs about 0.1 mm, tapering above midlength, apices acuminate; lower glumes 5-veined at the base, 3-veined at midlength; upper glumes 5-7-veined at the base; florets 3-4.5 mm long, 1-2 mm thick, obovoid; calluses 0.4-1 mm, sharp; lemmas indurate, densely and evenly pilose, hairs 2.5-6 mm, easily rubbed off, apices not lobed; awns 3-6 mm, rapidly deciduous, not geniculate, scabrous; paleas subequal to the lemmas in length and texture, glabrous, apices pinched; anthers 1.5-2 mm, penicillate, dehiscent, well-filled. |
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Caryopses | 3-4 mm, fusiform. |
2-3 mm. |
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Basal | sheaths glabrous or sparsely to densely pubescent, margins sometimes ciliate; collars glabrous or somewhat pubescent, without tufts of hair on the sides, collars of the flag leaves glabrous or sparsely pubescent; basal ligules 0.2-0.7 mm, membranous, truncate to rounded, usually not ciliate; upper ligules 1-1.5 mm, acute; blades (0.5)1.2-5 mm wide. |
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2n | = 36, 44. |
= 46, 48. |
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Achnatherum nelsonii |
Achnatherum hymenoides |
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Distribution |
AZ; CA; CO; ID; MT; NM; NV; OR; SD; TX; UT; WA; WY; AB; BC; SK; YT
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AR; AZ; CA; CO; ID; KS; MN; MT; ND; NE; NM; NV; OK; OR; SD; TX; UT; WA; WY; AB; BC; MB; SK; YT
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Discussion | Achnatherum nelsonii grows in meadows and openings, from sagebrush steppe and pinyon-juniper woodlands to subalpine forests, at 500-3500 m. It flowers in late spring to early summer, differing in this respect from A. perplexum. It is sometimes sympatric with A. lettermanii, from which it differs in its shorter paleas and wider leaves, and its tendency to grow in deeper or less disturbed soils. It differs from A. lemmonii in having wider leaf blades, shorter paleas, and membranous lemma lobes, and from A. nevadense and A. occidentale in its scabrous awns and the truncate to acute boundary of the glabrous tip of the callus with the callus hairs. The two subspecies intergrade to some extent. There is also intergradation with Achnatherum occidentale, possibly as a result of hybridization and introgression. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Achnatherum hymenoides grows in dry, well-drained soils, primarily in the western part of the Flora region and northern Mexico. Specimens from further east may be introduced; it is unknown whether they have persisted. The roots of A. hymenoides are often surrounded by a rhizosheath formed by mucilaginous secretions to which soil particles attach. This rhizosheath harbors nitrogen-fixing organisms that probably contribute to the success of the species as a colonizer. Native Americans used the seeds of Achnatherum hymenoides for food. It is also one of the most palatable native grasses for livestock. Several cultivars have been developed for use in restoration work, and it is becoming increasingly available for use as an ornamental. Achnatherum hymenoides forms natural hybrids with other members of the Stipeae. See discussion on p. 142. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 123. | FNA vol. 24, p. 139. | ||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Synonyms | Stipa williamsii, Stipa occidentalis var. nelsonii, Stipa nelsonii | Stipa hymenoides, Oryzopsis hymenoides | ||||
Name authority | (Scribn.) Barkworth | (Roem. & Schult.) Barkworth | ||||
Web links |
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