Poa arida
Poa chapmaniana
plains bluegrass, prairie speargrass
Chapman's blue grass
15-80 cm, erect or the bases decumbent, terete or weakly compressed;
nodes terete, 0-1 exserted.
5-30(40) cm tall, 0.3-0.7 mm thick, erect or the bases geniculate;
nodes terete, usually 1 exserted.
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 1/10 – 1/2 their length, terete or weakly compressed, smooth;
ligules 0.7-5 mm, decurrent, truncate to acute;
blades of innovations and culms similar, 2-5(8) cm long, 0.6-2.8 mm wide, flat or folded, thin, soft, smooth, margins scabrous, apices narrowly prow-shaped.
intra- and 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.
2-9.6 cm, erect, eventually open, moderately to densely congested, with 1-4(7) branches per node;
branches eventually ascending to spreading, rarely reflexed, terete, smooth or sparsely scabrous, spikelet-bearing to near the base or middle.
3.2-7 mm, lengths to 3.5(3.8) times widths, laterally compressed;
florets 2-7;
rachilla internodes smooth, sometimes sparsely puberulent.
(2)2.4-4.5 mm, laterally compressed;
florets (1)2-6;
rachilla internodes usually shorter than 0.7 mm, smooth or scabrous, 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.
subequal, about 3/4 as long as to subequal to the adjacent lemmas, lanceolate, thin, distinctly keeled, keels scabrous;
lower glumes 1-3-veined;
calluses webbed;
lemmas 1.9-3 mm, broadly lanceolate, distinctly keeled, smooth, keels and marginal veins short- to long-villous, hairs on the keels extending to near the apices, lateral veins obscure, usually softly puberulent, intercostal regions usually sparsely softly puberulent, apices obtuse to acute;
palea keels softly puberulent to long-villous at midlength, scabrous near the apices;
anthers 1, 0.1-0.2(0.3) mm.
= 56, 56+1, 56-58, 63, 64, 70, 76, 84, ca. 90, 95+-5, 100, 103.
= unknown.
Poa arida
Poa chapmaniana
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 chapmaniana is native from the central part of the Great Plains east and southward to the coast. It grows in dry to mesic forests, forest openings, and the margins of bottomlands, often in disturbed ground and on acidic substrates. Records from New York probably represent introductions. Its web and single short anther distinguish P. chapmaniana from P. annua (p. 520) and most plants of P. bigelovii. It also differs from P. bigelovii (see below), probably its closest relative, in having narrower leaf blades, and panicle branches that are eventually spreading.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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