Poa arida
Poa arctica
plains bluegrass, prairie speargrass
arctic bluegrass
15-80 cm, erect or the bases decumbent, terete or weakly compressed;
nodes terete, 0-1 exserted.
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.
closed for 1/10 – 1/5(1/4) their length, terete, smooth or sparsely scabrous, glabrous, bases of basal sheaths glabrous, distal sheath lengths (1.2)1.5-9(20) times blade lengths;
ligules (1)1.5-4(5) mm, smooth or sparsely to moderately scabrous, apices obtuse to acute;
blades strongly to gradually reduced in length distally, 1.5-5 mm wide, flat and moderately thin to folded and moderately thick and firm, abaxial surfaces smooth, adaxial surfaces smooth or sparsely to moderately scabrous, primarily over the veins, apices narrowly prow-shaped, flag leaf blades (0.4)1-7(10) cm.
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.
intra- and extravaginal.
mainly extravaginal.
(2.5)4-12(18) cm, erect, usually narrowly lanceoloid, contracted, sometimes interrupted, infrequently loosely contracted, usually congested, with 25-100 spikelets;
nodes with 1-5 branches;
branches 1-9 cm, erect to infrequently ascending, rarely spreading, terete to weakly angled, smooth or the angles sparsely to moderately scabrous, with 3-24 spikelets.
(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.
3.2-7 mm, lengths to 3.5(3.8) times widths, laterally compressed;
florets 2-7;
rachilla internodes smooth, sometimes sparsely puberulent.
(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.
lanceolate, distinctly keeled, smooth or sparsely scabrous;
lower glumes 3-veined;
calluses usually glabrous, infrequently webbed, hairs to 1/4 the lemma length;
lemmas 2.5-4.5 mm, lanceolate to narrowly lanceolate, distinctly to weakly keeled, keels and marginal veins short- to long-villous, lateral veins moderately prominent, glabrous or puberulent, intercostal regions usually glabrous, infrequently hairy, hairs to 0.3 mm, margins glabrous, apices acute or blunt;
palea keels scabrous, glabrous or short-villous at midlength, intercostal regions usually glabrous, sometimes puberulent to short-villous;
anthers 1.3-2.2 mm.
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.
= 56, 56+1, 56-58, 63, 64, 70, 76, 84, ca. 90, 95+-5, 100, 103.
= 36, 42, 56, 60, 62-68, 70, ca. 72, 74-76, 78-80, 82-84, 86, 88, 99, 106.
Poa arida
Poa arctica
Poa arida grows mainly on the eastern slope of the Rocky Mountains and in the northern Great Plains, primarily in riparian habitats of varying salinity or alkalinity. It is spreading eastward along heavily salted highway corridors. Reports of its occurrence west of the Continental Divide and in southwestern Texas are mostly attributable to misidentifications of P. arctica subsp. aperta (p. 530). P. arctica subsp. grayana (p. 532), and rhizomatous specimens of P. fendleriana (p. 556).
Poa arida may reflect past hybridization between P. secunda (p. 586) and a species of Poa sect. Poa. Poa glaucifolia Scribn. & T.A. Williams refers to specimens of the northern Great Plains that have a more lax growth form with broader leaves and occasionally somewhat open panicles, florets with a small web, and sometimes lacking hairs between the keel and marginal veins of the lemma. Plants with these characteristics have chromosome counts of 2ra = 56 and 70, whereas P. arida sensu stricto usually has 2n = 63, 64, or greater than 70. It is suspected that some of the variability reflects introgression from P. secunda.
Poa arida is a named intersectional hybrid
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
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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