Scientific Name
Achnatherum occidentale (Thurb.) Barkworth (Synonyms: Stipa occidentalis)
Common Name(s)
Western needlegrass
Tribe / Family Name
Stipeae
Flowering Period
June to August
Symbol
ACOC3
Description
Western needlegrass is a native cool-season perennial bunchgrass. Culms usually range from 14–120 cm in height. Its inflorescence is a narrow panicle 5–30 cm long with ascending branches, and occasionally loose and lax. Spikelets are appressed to the branches, 1-flowered, and awned (the lemma awns 15–55 mm long, twice-geniculate, twisted and plumose along the first two segments [hairs about 1 mm long], and glabrous to short plumose and not twisted along the terminal segment). Ligules are 0.2–1.5 mm long, membranous, often higher on the sides than the middle, truncate, entire to slightly erose-ciliolate, and occasionally lined with tufts of hairs continuing along the margins of the sheaths.
General Info
Western needlegrass can be found in dry mountain meadows, sagebrush steppe, western juniper and coniferous woodlands, rocky hills, plains, and montane to subalpine sites.
Similar Species
Western needlegrass looks similar to other needlegrass (Achnatherum) species, especially Thurber’s needlegrass (Achnatherum thurberianum). Both species have awns that are hairy along the first two segments, but can be differentiated from each other by inspecting the length of the ligules. Western needlegrass has ligules that are up to 2 mm long, and Thurber’s needlegrass has ligules that are 3–8 mm long. Also, western needlegrass has a straw-colored, papery glume, and Thurber’s needlegrass often has a purple-tinged, membranous glume.
Picture of growth habit.
Close-up picture of narrow panicle inflorescence.
Close-up picture of spikelet.
Close-up picture of lemma tip and awn hairs.
Close-up picture of subequal glumes.
Close-up picture of short, membranous ligule and hairs.
Illustration of western needlegrass. Glen Cole, 2017.