Poa lettermanii |
Poa unilateralis |
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Letterman's bluegrass |
San Francisco bluegrass |
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Habit | Plants perennial, 1–12 cm tall; densely cespitose. | Plants perennial, 5–40 cm long, frequently glaucous; densely cespitose. |
Basal branching | intra- and extravaginal or mainly intravaginal. |
intra- and extravaginal or mainly intravaginal. |
Leaves | sheaths closed to 25% of their length; ligules 1–3 mm; blades flat or folded, or slightly inrolled, 0.5–2 mm wide. |
sheaths closed 10(20)% of their length, bases of basal sheaths glabrous; ligules (0.8)2–6 mm long, blades of tillers usually 1–1.5 mm wide; thin; soon withering, distinctly narrower than those of the culm, infrequently broad and flat, or involute; cauline blades flat or folded, 2–5 mm wide; soft; thin and soon withering or moderately thick and somewhat fleshy and retaining their form; smooth; blades gradually reduced in length higher on the culm. |
Inflorescences | erect, contracted, 1–3 cm long, usually exserted from the sheaths; branches erect to steeply ascending; slender; to 1.5 cm. |
erect, nearly cylindrical, contracted, 3–7 cm; spikelets (20)30–80(120); branches 0.5–1.5(4.5)cm long, 3–7 per node, densely papillose and sparsely scabrous. |
Spikelets | 3–4 mm, green or purple; florets 2–3; rachilla internodes less than 1 mm long; smooth. |
lanceolate to narrowly ovate; to 3.5 times as long as wide, 4.5–7 mm; florets 3–5. |
Glumes | lanceolate to broadly lanceolate, 2.4– 3.6(4) mm, usually equaling or exceeding the lowest lemma, frequently exceeding the upper florets; lower glumes 3-veined. |
lanceolate, slightly unequal; keels smooth and papillate or scabrous; lower glumes 3-veined. |
Calluses | glabrous. |
glabrous or with a crown of tiny crisp hairs around the base; hairs 0.1–0.2 mm long. |
Lemmas | lanceolate, 2.5–3 mm long, distinctly keeled; thin, glabrous; keels and marginal veins rarely sparsely puberulent; tips acute. |
lanceolate, distinctly keeled, 3–4.5 mm, glabrous, or keels and marginal veins short-villous on proximal half, sparsely crisply puberulent near the base; margins glabrous; tips acute. |
Anthers | 0.2–0.8 mm. |
1.5–3 mm. |
2n | =14. |
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Poa lettermanii |
Poa unilateralis |
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Distribution | ||
Discussion | Rocky alpine ridges and ledges. 2900–3100m. Casc. CA, ID, NV, WA; north to British Columbia, east to CO. Native. This is a small, cespitose, alpine bluegrass, most similar to P. suksdorfii. Both have subequal glumes that tend to be longer than the lowest lemma, but P. suksdorfii has larger spikelets with longer glumes. In Oregon, P. lettermanii is known only from high elevation on South Sister in the central Cascades. |
2 subspecies. Poa unilateralis is a cespitose grass with dense inflorescences that grows on coastal headlands. Its leaf sheaths are open most of their length, and its calluses are glabrous or nearly so. |
Source | Flora of Oregon, volume 1, page 459 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting |
Flora of Oregon, volume 1, page 467 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting |
Sibling taxa | ||
Subordinate taxa | ||
Web links |
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