Poa arida
Poa sublanata
plains bluegrass, prairie speargrass
cottonball bluegrass
15-80 cm, erect or the bases decumbent, terete or weakly compressed;
nodes terete, 0-1 exserted.
20-40(75) cm, erect or the bases decumbent, not branching above the base, terete or weakly compressed;
nodes terete, proximal nodes usually not 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 2/5 – 1/2 their length, terete, glabrous, smooth or slightly scabrous, bases of basal sheaths glabrous, distal sheath lengths (1)1.2-3.5 times blade lengths;
collars smooth, glabrous;
ligules 1.5-4(6) mm, smooth, apices obtuse to acute, not ciliate;
blades 1-3.5(5) mm wide, folded or flat, innovation shoot blades involute, soft, abaxial surfaces glabrous, adaxial surfaces smooth or sparsely scabrous, frequently sparsely hairy with 0.2-0.8 mm hairs, slender, erect to appressed, curving, sinuous or straight, apices narrowly prow-shaped, cauline blades subequal, flag leaf blades 1.5-8 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.
5-9(17) cm, narrowly lanceoloid to narrowly pyramidal, loosely contacted to open, sparse, with 25-60 spikelets and 2-5 branches per node;
branches 1-3 cm, ascending to spreading, slightly flexuous to fairly straight, terete, smooth or sparsely scabrous, usually with 1-5 spikelets per branch, the spikelets moderately crowded in the distal 1/2.
3.2-7 mm, lengths to 3.5(3.8) times widths, laterally compressed;
florets 2-7;
rachilla internodes smooth, sometimes sparsely puberulent.
4-6.5(8) mm, lengths to 3 times widths, laterally compressed;
florets 2-4(6);
rachilla internodes shorter than 1 mm, smooth, usually glabrous, rarely with a few hairs.
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.
unequal to subequal, usually distinctly shorter than the adjacent lemmas, lanceolate, distinctly keeled, keels smooth to sparsely scabrous;
lower glumes 2.8-3.5 mm, narrowly lanceolate, (1)3-veined;
upper glumes 4-4.5(5) mm, distinctly shorter than to nearly equaling the lowest lemmas;
calluses dorsally webbed, webs copious, hairs at least 1/2 times the lemma length, sometimes secondary webs present under the marginal veins;
lemmas 3.7-4.5(5) mm, lanceolate, usually strongly purple, distinctly keeled, keels, lateral veins, and marginal veins copiously hairy, hairs cottony, lateral veins prominent, less hairy, intercostal regions glabrous, usually smooth or finely muriculate, sometimes sparsely scabrous distally, margins narrowly hyaline, glabrous, apices acute;
palea keels sparsely scabrous, long-villous at midlength, intercostal regions narrow, glabrous;
anthers 1.8-2.5 mm.
= 56, 56+1, 56-58, 63, 64, 70, 76, 84, ca. 90, 95+-5, 100, 103.
= 56, ca. 70.
Poa arida
Poa sublanata
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 sublanata grows in the high arctic of Alaska and Russia, usually on sandy ground. Bulbiferous plants are known from Russia; none have been found in the Flora region.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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