Poa howellii |
Poa pratensis |
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Howell's bluegrass |
Kentucky bluegrass |
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Habit | Plants annual, rarely perennial, (10)25– 80(120) cm tall; densely cespitose. | Plants perennial, 5–70(100)cm tall, densely to loosely cespitose and extensively rhizomatous. |
Basal branching | intravaginal. |
mainly extravaginal or equally extra- and intravaginal. |
Leaves | sheaths closed 50% or more of their length; ligules 1.5–5(10)mm, blades of tillers flat, 1–7(10) mm wide, finely scabrous; cauline blades 2–10 cm. |
sheaths closed 25–50% of their length, bases of basal sheaths glabrous; collars smooth, glabrous; ligules truncate to rounded, 0.9–2(3.1)mm, blades of extravaginal shoots like cauline blades, those of intravaginal shoots; when present, sometimes distinctly narrower; flat to involute, 0.4–1 mm wide; cauline blades flat or folded; to involute on the margins, 0.4–4.5 mm wide; lower surfaces smooth, glabrous; upper surfaces smooth or sparsely scabrous, frequently with sparse; slender hairs 0.2–0.8 mm long; uppermost blades 1.5–10 cm. |
Inflorescences | erect, eventually open, 10–25(30)cm; the branches eventually spreading or reflexed. |
narrowly ovoid to narrowly or broadly pyramidal, loosely contacted to open, sparsely to moderately congested, 2–15(20)cm; spikelets (25)30–100+; branches spreading; (1)2–9 cm long; (1)2–7(9) per node; spikelets 4–30(50), usually fairly crowded in distal half. |
Spikelets | (2)4– 6 mm; florets 2–5; rachilla internodes about 1 mm; smooth, softly puberulent or occasionally glabrous. |
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Glumes | slightly unequal; keels and sometimes lateral veins scabrous; lower glumes 1–3-veined. |
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Culm(s) | nodes terete. |
nodes terete or slightly compressed, 1–2(3) nodes exposed. |
Calluses | with sparse cobwebby hairs on at least some florets. |
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Lemmas | lanceolate to narrowly lanceolate, 2.5– 3.5 mm, distinctly keeled, evenly crisply puberulent near the base, finely scabrous distally; margins narrowly hyaline; tips narrowly acute, rarely purple. |
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Anthers | 0.2–1 mm. |
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Poa howellii |
Poa pratensis |
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Distribution | ||
Discussion | Open, often moist woods and bottomlands, often with moss or boulders. 0–1100m. Casc, ECas, Sisk, WV. CA, WA; north to British Columbia. Native. |
6 subspecies; 5 subspecies treated in Flora. Poa pratensis is a common grass with slightly nodding inflorescences and copious cobwebby callus hairs. Poa rhizomata, of rocky ultramafic slopes in southwestern Oregon, is similar but has sparse inflorescences, acute ligules, and unisexual inflorescences. Poa confinis of coastal sands has glabrous (to sparsely hairy) lemmas and diffuse, not tufted callus hairs. Poa wheeleri, a common eastern Oregon species, lacks the lemma hairs and has denser inflorescences and more strongly scabrous leaf sheaths. Poa pratensis is common, polyploid, and highly variable. It hybridizes with related taxa including P. alpina, P. secunda, and P. wheeleri. The resulting variation in P. pratensis can be perpetuated through both sexual and asexual seed production, resulting in many recognizable forms that are linked by intermediates. Most or all Poa pratensis found in Oregon are descended from three introduced subspecies (P. p. ssp. angustifolia, P. p. ssp. pratensis, and P. p. ssp. irrigata). |
Source | Flora of Oregon, volume 1, page 457 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting |
Flora of Oregon, volume 1, page 462 Rob Soreng, Barbara Wilson, Richard Brainerd, Nick Otting |
Sibling taxa | ||
Subordinate taxa | ||
Web links |
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