Achnatherum occidentale

(Thurb.) Barkworth
Synonyms: Stipa occidentalis unknownStipa occidentalis var. montana unknown
Treatment appears in FNA Volume 24. Treatment on page 121.
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. 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. Panicles 5-30 cm long, 0.5-1.5 cm wide; branches appressed, straight, longest branches 1-7 cm. Spikelets appressed to the branches. 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. Caryopses 4-6 mm, fusiform. 2n =36.

Distribution

Utah, Wash., Colo., Mont., Alta., B.C., Idaho, Calif., Wyo., Ariz., Nev., Oreg.

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.

References

None.

Key

1 Terminal awn segment usually pilose; culms 0.3-1 mm thick, glabrous even on the basal internodes; glumes often purplish Achnatherum occidentale subsp. occidentale
1 Terminal awn segment usually scabrous or glabrous, occasionally pilose at the base; culms 0.5-2 mm thick; glumes usually green. > 2
2 First 2 awn segments scabrous or pilose with hairs of mixed lengths; apical lemma hairs longer than the basal awn hairs Achnatherum occidentale subsp. californicum
2 First 2 awn segments pilose, the hairs gradually and evenly becoming shorter towards the first geniculation; apical lemma hairs similar in length to the basal awn hairs Achnatherum occidentale subsp. pubescens