Poa lettermanii |
Poa laxa |
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Letterman bluegrass, Letterman's blue grass |
banff bluegrass, glaucous bluegrass, lax bluegrass, Mt. Washington bluegrass, wavy blue grass |
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Habit | Plants perennial; not glaucous; densely tufted, not stoloniferous, not rhizomatous. | Plants perennial; not or only slightly glaucous; densely tufted, not stoloniferous, not rhizomatous. | ||||
Culms | 1-12 cm, slender. |
8-35 cm tall, 0.5-0.9 mm thick, ascending to erect, slender; nodes terete, 0(1) exserted. |
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Sheaths | closed for 1/6 – 1/4 their length, terete; ligules 1-3 mm, milky white to hyaline, smooth; blades 0.5-2 mm wide, flat or folded, or slightly inrolled, thin, without papillae (at 100x), apices narrowly prow-shaped. |
closed for 1/5-1/3 their length, terete, smooth, glabrous, bases of basal sheaths glabrous; collars smooth or scabrous, glabrous; ligules 2-4 mm, smooth, apices acute, often lacerate; innovation blades similar to the cauline blades; cauline blades 1-2(3) mm wide, flat, thin, soft, smooth, narrowly prow-tipped, blades not strongly graduated or reduced upwards. |
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Basal branching | all or mainly intra-vaginal. |
mixed, mainly extravaginal or mainly pseudointravaginal, sometimes intravaginal. |
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Panicles | 1-3 cm, erect, contracted, usually exserted from the sheaths; branches to 1.5 cm, erect to steeply ascending, slender, sulcate or angled, smooth or the angles sparsely scabrous; pedicels shorter than the spikelets. |
2-8 cm, slightly lax, usually loosely contracted and sparse, infrequently contracted and dense; nodes with 1-3(5) branches; branches 1-3(4) cm, usually ascending or weakly spreading, infrequently erect, fairly straight or flexuous, slender, sulcate or angled, smooth or the angles sparsely scabrous, with 1-8 spikelets. |
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Spikelets | 3-4 mm, laterally compressed, green or anthocyanic; florets 2-3; rachilla internodes shorter than 1 mm, smooth. |
4-6 mm, lengths to 3 times widths, laterally compressed; florets 2-5; rachilla internodes shorter than 1 mm, smooth, glabrous. |
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Glumes | usually equaling or exceeding the lowest lemmas, sometimes also equaling or exceeding the upper florets, lanceolate to broadly lanceolate, distinctly keeled, keels smooth; lower glumes 3-veined; calluses glabrous; lemmas 2.5-3 mm, lanceolate, distinctly keeled, thin, usually glabrous, keels and marginal veins rarely sparsely puberulent proximally, apices acute; palea keels scabrous; anthers 0.2-0.8 mm. |
nearly equaling or slightly longer than the adjacent lemmas, lanceolate to broadly lanceolate, thin, distinctly keeled, keels smooth or sparsely scabrous; lower glumes 1-3-veined; upper glumes shorter than or subequal to the lowest lemmas; calluses glabrous or webbed, hairs usually shorter than 1/4 the lemma length, sparse; lemmas 3-4.6 mm, lanceolate to broadly lanceolate, thin, distinctly keeled, keels and marginal veins short- to long-villous, lateral veins glabrous or sparsely softly puberulent, lateral veins obscure, intercostal regions glabrous, margins glabrous, apices acute; paleas sparsely scabrous over the keels; anthers (0.6)0.8-1.1(1.3) mm. |
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2n | = 14. |
= 28, 42, 84. |
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Poa lettermanii |
Poa laxa |
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Distribution |
CA; CO; ID; MT; NV; OR; UT; WA; WY; AB; BC
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CO; ME; MT; NH; NY; OR; VT; WY; AB; BC; NL; QC |
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Discussion | Poa lettermanii grows on rocky slopes of the highest peaks and ridges in the alpine zone, from northern British Columbia to western Alberta and south to California and Colorado, usually in the shelter of rocks or on mesic to wet, frost-scarred slopes. It is one of only three known diploid Poa species native to the Western Hemisphere. Its glabrous calluses and lemmas usually distinguish it from P. abbreviata (p. 582); it also differs in having flat or folded leaf blades, and shorter spikelets with glumes that are longer than the adjacent florets. Poa montevansii E.H. Kelso is tentatively included here, although its slightly longer lemmas that slightly exceed the glumes suggest that it may represent rare, glabrous forms of P. abbreviata. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Poa laxa is a low arctic to high alpine amphiatlantic species. It has been treated as a series of separate species, but the differences seem relatively minor and incomplete. Its short anthers and smoother branches usually distinguish it from P. glauca (p. 576), with which it can hybridize to form P. laxa x glauca (p. 572). Poa laxa has four subspecies, two of which are native to the Flora region; subsp. laxa grows in central Europe; and subsp. flexuosa (Sm.) Hyl. in northwestern Europe. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 580. | FNA vol. 24, p. 570. | ||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Abbreviatae | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Oreinos | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Synonyms | P. mor.tevansi | |||||
Name authority | Vasey | Haenke | ||||
Web links |
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