Achnatherum occidentale |
Achnatherum ×bloomeri |
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common western needlegrass, stiff needlegrass, velvet-leaf, western needle grass |
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Habit | Plants tightly cespitose, not rhizomatous. | |||||||||
Culms | 14-120(180) cm tall, 0.3-2 mm thick, internodes glabrous or puberulent to densely pubescent; nodes 2-4, glabrous or pubescent. |
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Panicles | 5-30 cm long, 0.5-1.5 cm wide; branches appressed, straight, longest branches 1-7 cm. |
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Spikelets | appressed to the branches. |
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Glumes | subequal, 9-15 mm long, 0.6-0.9 mm wide; florets 5.5-7.5 mm long, 0.5-0.9 mm thick, fusiform, terete; calluses 0.8-1.2 mm, sharp, dorsal boundary of the glabrous tip with the callus hairs narrowly acute; lemmas evenly hair, hairs 0.5-1.5 mm at midlength, apical hairs somewhat longer than those below, sometimes similar in length to those at the base of the awns, sometimes longer, apical lobes 0.3-0.5 mm, membranous; awns 15-55 mm, twice-geniculate, first 2 segments evidently hairy, terminal segment glabrous or partly to wholly pilose, sometimes scabrous; paleas 2.2-3.5 mm, 2/5 – 3/5 as long as the lemmas, hairs at the tip usually shorter than 1 mm, frequently extending beyond the apices, apices rounded; anthers 2.5-3.5 mm, dehiscent, not penicillate. |
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Caryopses | 4-6 mm, fusiform. |
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Basal | sheaths glabrous or puberulent to densely pubescent, often ciliate at the throat; collars often with tufts of hair at the sides; ligules 0.2-1.5 mm, often ciliate; blades 0.5-3 mm wide and flat, or convolute and 0.1-0.8 mm in diameter, lax to straight. |
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2n | =36. |
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Achnatherum occidentale |
Achnatherum ×bloomeri |
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Distribution |
AZ; CA; CO; ID; MT; NV; OR; UT; WA; WY; AB; BC
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AZ; CA; CO; ID; MT; NM; NV; OR; UT; WA; WY |
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Discussion | Achnatherum occidentale, which extends from British Columbia to California, Utah, and Colorado, varies considerably in pubescence and size. The three subspecies recognized here occasionally occur together. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Achnatherum ×bloomeri and other hybrids involving A. hymenoides Numerous natural hybrids exist between Achnatherum hymenoides and other members of the Stipeae. Johnson (1945, 1960, 1962, 1963, 1972) described several of these; all are sterile. Using the treatment adopted here, Johnson's hybrids have as the second parent A. occidentale (all subspecies), A. thurberianum, A. scribneri, A. robustum, Jarava speciosa, and Nassella viridula. Evidence from herbarium specimens suggests that A. hymenoides also forms sterile hybrids with other species of Achnatherum. The name Achnatherum ×bloomeri applies only to hybrids between A. hymenoides and A. occidentale subsp. occidentale, but plants keying here may include any of the other interspecific hybrids. They all differ from A. hymenoides in having more elongated florets and awns 10-20 mm long, and from their other parent, in most instances, in having longer lemma hairs and more saccate glumes. Identification of the second parent is best made in the field by noting which other species of Stipeae are present, bearing in mind that species that are not in anthesis at the same time in one year might have sufficient overlap for hybridization in other years. Of the two intergeneric hybrids mentioned above, that with Nassella viridula is treated as ×Achnella caduca (see p. 169). It differs from Achnatherum hymenoides in its longer glumes and florets, and from other A. hymenoides hybrids in having a readily deciduous awn. No binomial has been proposed for the hybrid with Jarava speciosa. There is one fertile intergeneric hybrid involving A. hymenoides, A. contractum. It is included in Achnatherum and described below because it resembles other members of Achnatherum more than it does Piptatherum, the genus of the other parent. Sterile hybrids have anthers that do not dehisce, and contain few, poorly formed pollen grains. They also fail to form good caryopses, but this is also true of some non-hybrid plants. In the case of non-hybrid plants, failure to form good caryopses can result from failure to capture pollen or from incompatibility between the pollen grain and the pistillate plant. It is not known which, if either, of these explanations accounts for the large number of empty caryopses found in Achnatherum hymenoides. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 121. | FNA vol. 24, p. 142. | ||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum | ||||||||
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Subordinate taxa | ||||||||||
Synonyms | Stipa occidentalis, Stipa occidentalis var. montana | genus ×stiporyzopsis bloomeri, Oryzopsis ×bloomeri, Stipa bloomeri | ||||||||
Name authority | (Thurb.) Barkworth | (Bol.) Barkworth | ||||||||
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