Poa arida
Poa sylvestris
plains bluegrass, prairie speargrass
woodland bluegrass
15-80 cm, erect or the bases decumbent, terete or weakly compressed;
nodes terete, 0-1 exserted.
30-120 cm, bases often decumbent.
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 (1/20) 1/2-7/8 their length, terete, throats frequently ciliate near the point of fusion;
ligules 0.5-2.7 mm, smooth or sparsely scabrous, truncate to obtuse;
blades 0.7-5 mm wide, flat, thin, lax.
intra- and extravaginal.
mainly pseudointravaginal.
(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.
(6.7)9-20 cm, open, narrowly conical at maturity;
nodes with (2)3-10 branches per node;
branches (2)3-7 cm, spreading to eventually reflexed, straight, angled, angles several, densely scabrous, with 1-11 spikelets.
3.2-7 mm, lengths to 3.5(3.8) times widths, laterally compressed;
florets 2-7;
rachilla internodes smooth, sometimes sparsely puberulent.
2.5-4.4 mm, laterally compressed;
florets 2-3(4);
rachilla internodes longer than (1)1.2 mm, smooth, glabrous.
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.
distinctly keeled, keels scabrous;
lower glumes 1(3)-veined;
upper glumes shorter than or subequal to the lowest lemmas;
calluses webbed;
lemmas 2.1-3.1 mm, broadly lanceolate, distinctly keeled, keels and marginal veins short-villous, extending to near the apices on the keels, lateral veins prominent, softly puberulent to short-villous, intercostal regions usually sparsely softly puberulent, smooth, apices obtuse to acute;
palea keels softly puberulent at midlength, apices finely scabrous;
anthers 1-1.8 mm.
= 56, 56+1, 56-58, 63, 64, 70, 76, 84, ca. 90, 95+-5, 100, 103.
= 28.
Poa arida
Poa sylvestris
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 sylvestris grows in southeastern Canada and throughout much of the eastern United States, mainly at low elevations in woodlands, especially in riparian zones. It is easily distinguished from P. wolfii (p. 514) by its smaller, more numerous spikelets and lemmas that are usually sparsely hairy between the veins. Plants from the middle Appalachian Mountains have been confused with P. paludigena (p. 572); P. sylvestris is usually larger, has more than 2 branches per panicle node, is pubescent between the lemma veins and palea keels, and has larger anthers.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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