Poa arctica
Poa wheeleri
arctic bluegrass
Hooker's bluegrass, Wheeler's blue grass
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.
35-80 cm, erect or the bases decumbent, terete or weakly compressed;
nodes terete, 1-2 exserted.
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 1/3-1/4 their length, terete to slightly compressed, at least some proximal sheaths densely retrorsely scabrous, hispidulous, or softly puberulent for the upper 1/4 of their length, bases of basal sheaths glabrous, distal sheath lengths (1.4)1.7-4.6(6.2) times blade lengths;
collars of proximal leaves glabrous or with hairs the same length as those of their sheaths;
ligules 0.5-2 mm, smooth or scabrous, sometimes puberulent, truncate, those of the lower culm and innovation leaves 0.5-1.5 mm, abaxial surfaces scabrous to softly puberulent, truncate;
innovation blades folded or involute, infrequently flat, moderately thick, soft, adaxial surfaces usually densely scabrous to hispidulous;
cauline blades 2-3.5 mm wide, flat or folded, smooth or sparsely scabrous, glabrous or hispidulous, apices narrowly to broadly prow-shaped, blades gradually reduced distally or the middle blades longest, flag leaf blades 1-10 cm long.
mainly extravaginal.
mainly extra-vaginal.
(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.
5-12(18) cm, erect or nodding, ovoid to pyramidal, loosely contracted to open, with 20-70 spikelets, proximal internodes usually shorter than 3.5 cm;
nodes with 2-5 branches;
branches (1)1.7-6.5 cm, ascending to spreading or reflexed, lax, terete or weakly angled, sparsely to moderately scabrous, with 2-8(12) 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.
5.5-10 mm, lengths to 3.5 times widths, laterally compressed, not sexually dimorphic;
florets 2-7;
rachilla internodes smooth or scabrous, glabrous or sparsely to densely hispidulous.
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.
1/4 - 2/3(3/4) as long as the adjacent lemmas, lanceolate, distinctly keeled;
lower glumes 1-3-veined, 1/4-1/2 as long as the adjacent lemmas;
calluses glabrous;
lemmas 3-6 mm, lanceolate, distinctly keeled, keels and marginal veins glabrous or softly puberulent to short-villous, intercostal regions glabrous or hispidulous, infrequently puberulent, smooth or finely scabrous, lateral veins obscure to moderately prominent, margins glabrous, apices acute;
palea keels scabrous, intercostal regions glabrous;
anthers usually vestigial (0.1-0.2 mm) or aborted late in development and up to 2 mm, rarely normal.
= 36, 42, 56, 60, 62-68, 70, ca. 72, 74-76, 78-80, 82-84, 86, 88, 99, 106.
= 56, 61, 62, 63, 64, 66, 61, 70, ca. 74, 75, 79, 80, 81, 87, 89, 90, 91.
Poa arctica
Poa wheeleri
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 wheeleri is common at mid- to high elevations, generally on the east side of the coastal mountains from British Columbia to California, and from Manitoba to New Mexico. It generally grows in submesic coniferous forests to subalpine habitats. Most plants have densely retrorsely pubescent or scabrous sheaths, involute innovation blades that are pubescent adaxially, and pistillate florets.
Poa wheeleri, a high polyploid apomictic species, probably arose from hybridization between P. cusickii (p. 559) and another member of the Poa nervosa complex. It resembles P. rhizomata (see next) and P. chambersii (p. 548) more than P. nervosa sensu stricto (see previous). It differs from P. chambersii in having at least some proximal sheaths that are densely retrorsely scabrous or pubescent (sometimes obscurely so), and folded or involute innovation blades that are scabrous to hispidulous on the adaxial surfaces. For a comparison with P. nervosa, see p. 545. Natural hybrids have been found between P. wheeleri and P. pratensis (p. 522).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants lacking well-developed rhizomes; anthers aborted late in development; plants of the high arctic | subsp. caespitans |
1. Plants usually with well-developed rhizomes; anthers normal or plants not of the high arctic. | → 2 |
2. Panicles erect, the branches relatively stout, fairly straight; longest branches of the lowest panicle nodes 1/4-1/2 the length of the panicles; culms wiry, usually several together; calluses glabrous or shortly webbed; paleas sometimes glabrous; plants glaucous, growing in the southern Rocky-Mountains and adjacent portions of the Intermountain region | subsp. aperta |
2. Panicles lax to erect, the branches slender, flexuous to fairly stout and straight; longest branches of the lowest panicle nodes 2/5 – 3/5 the length of the panicles; culms slender to stout, varying from solitary to several together; calluses glabrous or webbed, the hairs usually more than 1/2 as long as the lemmas; paleas pubescent; plants sometimes glaucous, widespread in distribution. | → 3 |
3. Calluses glabrous; spikelets not bulbiferous | subsp. grayana |
3. Calluses webbed, often copiously so, sometimes glabrous in bulbiferous spikelets; spikelets sometimes bulbiferous. | → 4 |
4. Spikelets (5)6-8 mm long; lemmas 4-6 mm long; blades 2-6 mm wide; rachillas usually hairy; plants primarily of the western arctic, extending to northwestern British Columbia | subsp. lanata |
4. Spikelets (3.5)4-7 mm long; lemmas (2.7)3-4.5 mm long; blades 1.5-3 mm wide; rachillas commonly glabrous; plants widespread | subsp. arctica |
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