Poa arctica |
Poa laxa |
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arctic bluegrass |
banff bluegrass, glaucous bluegrass, lax bluegrass, Mt. Washington bluegrass, wavy blue grass |
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Habit | Plants perennial; usually strongly anthocyanic; rhizomatous, rhizomes usually well developed, sometimes poorly developed, shoots usually solitary. | Plants perennial; not or only slightly glaucous; densely tufted, not stoloniferous, not rhizomatous. | ||||||||||||||||||||
Culms | 7.5-60 cm, slender to stout, terete or weakly compressed, bases usually decumbent, not branching above the bases; nodes terete, proximal nodes usually not exserted, 0-2 exserted above. |
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)1/5 – 2/5 their length, terete, glabrous, smooth or sparsely scabrous, bases of basal sheaths glabrous, distal sheath lengths 1.4-4(5.3) times blade lengths; collars smooth, glabrous; ligules (1)2-7 mm, glabrous, smooth or sparsely to infrequently moderately scabrous, apices usually rounded to obtuse or acute, rarely truncate, entire or lacerate; blades 1-6 mm wide, flat or folded, somewhat involute, smooth, glabrous, apices broadly prow-shaped, cauline blades subequal or gradually reduced distally, flag leaf blades 0.7-9 cm. |
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 | mainly extravaginal. |
mixed, mainly extravaginal or mainly pseudointravaginal, sometimes intravaginal. |
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Panicles | (2)3.5-15 cm, ovoid to broadly pyramidal, usually open, sparse, with 10-40(60) spikelets, proximal internodes shorter than 1.5(3) cm, with (1)2-5 branches per node; branches 1.5-6 cm, spreading soon after emergence from the sheath, thin, sinuous, and flexuous to fairly stout and straight, terete, smooth or sparsely to infrequently moderately scabrous, with (1)2-5 spikelets, the spikelets not crowded. |
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 | (3.5) 4.5-8 mm, lengths to 3.5 times widths, laterally compressed, sometimes bulbiferous; florets (2)3-6, infrequently bulb-forming; rachilla internodes smooth or muriculate, proximal internodes glabrous or sparsely softly puberulent to long-villous. |
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 | lanceolate to broadly lanceolate, distinctly or weakly keeled, keels usually smooth, sometimes sparsely scabrous distally, lateral veins usually moderately pronounced; lower glumes (3)3.5-5(6) mm, 3-veined; upper glumes 3.5-5.5(6.5) mm, nearly equaling to slightly exceeding the lowest lemmas, or distinctly shorter; calluses glabrous or webbed, hairs sparse and short to over 1/3 – 2/3 the lemma length; lemmas (2.7)3-6(7) mm, lanceolate to broadly lanceolate, usually strongly purple, distinctly keeled, keels, marginal veins, and lateral veins long-villous, hairs on the lateral veins sometimes shorter, lateral veins prominent, intercostal regions short-villous to softly puberulent at least near the base, glabrous elsewhere, smooth to weakly muriculate and/or usually sparsely scabrous, infrequently moderately scabrous, margins broadly hyaline, glabrous, apices acute; palea keels usually short- to long-villous for most of their length, rarely nearly glabrous and scabrous, intercostal regions broad, usually at least sparsely softly puberulent, rarely glabrous, apices scabrous; anthers 1.4-2.5 mm, sometimes aborted late in development. |
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 | = 36, 42, 56, 60, 62-68, 70, ca. 72, 74-76, 78-80, 82-84, 86, 88, 99, 106. |
= 28, 42, 84. |
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Poa arctica |
Poa laxa |
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Distribution |
AK; CO; ID; MT; NM; NV; UT; WA; WY; AB; BC; MB; NL; NT; NU; ON; QC; SK; YT; Greenland
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CO; ME; MT; NH; NY; OR; VT; WY; AB; BC; NL; QC |
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Discussion | Poa arctica is a common circumboreal species of arctic and alpine regions, growing mainly in mesic to subhydric, acidic tundra and alpine meadows, and on rocky slopes. It extends south in the Rocky Mountains to New Mexico. The frequency of sterile anthers in plants of the high arctic suggests that P. arctica is sometimes apomictic in that region. Over most of the rest of its range, P. arctica usually develops normal anthers. This and isozyme data for populations from alpine and low arctic regions suggest sexual reproduction is common in these habitats. The most reliable way to distinguish Poa arctica from P. pratensis (p. 522), particularly subsp. alpigena, is by the wider paleas and the presence of hairs between the palea keels. Bulbiferous forms of P. arctica differ from P. stenantha var. vivipara (p. 594) in not being glaucous, and in having rhizomes and terete, smooth panicle branches. Poa xgaspensis (p. 601) also resembles P. arctica, but it has sharply keeled, more scabrous glumes and a spikelet shape that is intermediate between P. pratensis and P. alpina (p. 518). Poa arctica forms natural hybrids with both P. pratensis and P. secunda (p. 586). (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. | FNA vol. 24, p. 570. | ||||||||||||||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Poa | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Oreinos | ||||||||||||||||||||
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Name authority | R. Br. | Haenke | ||||||||||||||||||||
Web links |