Poa cusickii |
Poa arachnifera |
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Cusick's bluegrass |
Texas bluegrass |
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Habit | Plants perennial; usually densely tufted, rarely moderately densely tufted, usually neither rhizomatous nor stoloniferous, infrequently short-rhizomatous or stoloniferous, rarely with distinct rhizomes. | Plants perennial; loosely tufted, rhizomatous, rhizomes slender. | ||||||||||||
Culms | 10-60(70) cm tall, 0.5-1.8 mm thick, erect or the bases decumbent, terete or weakly compressed; nodes terete, 0-2 exserted. |
20-85 cm, erect, terete or weakly compressed; nodes terete, 0-1 exserted. |
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Sheaths | closed for 1/4-3/4 their length, terete, smooth or scabrous, glabrous, bases of basal sheaths glabrous, distal sheath lengths 1.6-10 times blade lengths; collars smooth or scabrous, glabrous; ligules of cauline leaves 1-3(6) mm, smooth or scabrous, truncate to acute, ligules of the innovation leaves 0.2-0.5(2.5) mm, scabrous, usually truncate; innovation blades sometimes distinctly different from the cauline blades, 0.5-2 mm wide, involute, moderately thick, moderately firm, adaxial surfaces usually densely scabrous or hispidulous to softly puberulent, infrequently nearly smooth and glabrous; cauline blades subequal or the midcauline blades longest or the blades gradually reduced in length distally, 0.5-3 mm wide, flat, folded, or involute, usually thin, usually withering, abaxial surfaces smooth or scabrous, apices narrowly to broadly prow-shaped, flag leaf blades 0.5-5(6) cm. |
closed firmly for 1/7-1/3 their length, sometimes for a longer distance by a hyaline membrane, terete, smooth, glabrous, bases of basal sheaths glabrous; ligules 1-4 mm, smooth or scabrous; innovation blades 10-35 cm long, 1-3.5 mm wide; cauline blades 2-25 cm long, 1.5-4.5 mm wide, flat or folded, lax, both surfaces smooth or sparsely finely scabrous, glabrous, apices narrowly to broadly prow-shaped. |
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Basal branching | intravaginal or intra- and extravaginal. |
intra- and extravaginal. |
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Panicles | 2-10(12) cm, usually erect, contracted or loosely contracted, narrowly lanceoloid to ovoid, congested or moderately congested, with 10-100 spikelets and 1-3(5) branches per node; branches 0.5-4(5) cm, erect or steeply ascending, fairly straight, slender to stout, terete to angled, smooth or scabrous, with 1-15 spikelets. |
3-12(18) cm, erect, narrowly cylindrical, often interrupted or lobed, congested, with (70)100-200 spikelets; nodes with (2)3-7(9) branches; branches 1-3(5) cm, erect to slightly ascending, terete or weakly angled, sparsely to densely coarsely scabrous, with 8-30 spikelets. |
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Spikelets | (3)4-10 mm, lengths to 3 times widths, broadly lanceolate to narrowly ovate, laterally compressed, not sexually dimorphic; florets 2-6; rachilla internodes 0.5-1.2 mm, smooth or scabrous. |
4-8(10) mm, sexually dimorphic, laterally compressed, pistillate spikelets larger, with fewer florets and more pubescence than the staminate spikelets; florets 2-10; rachilla internodes smooth. |
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Glumes | lanceolate, distinctly keeled; lower glumes 3-veined, distinctly shorter than the lowest lemmas; calluses glabrous or diffusely webbed, hairs less than 1/4 the lemma length; lemmas (3)4-7 mm, lanceolate to broadly lanceolate, distinctly keeled, membranous to thinly membranous, smooth or sparsely to densely scabrous, glabrous or the keels and/or marginal veins puberulent proximally, lateral veins obscure to prominent, margins glabrous, apices acute; palea keels scabrous, intercostal regions glabrous; anthers vestigial (0.1-0.2 mm), aborted late in development, or 2-3.5 mm. |
unequal, distinctly keeled, keels and lateral veins scabrous; lower glumes 1-3-veined. |
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Pistillate florets | calluses copiously 3-webbed, hairs 4-10 mm, mostly silky, plicate; lemmas 4.2-6.4 mm, lanceolate, 5-7 veined, distinctly keeled, glabrous, or the keels and marginal veins, sometimes also the lateral veins, densely long-villous, margins glabrous, apices acute; palea keels scabrous, glabrous or sometimes softly puberulent to long-villous at midlength. |
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Staminate florets | calluses glabrous or sparsely dorsally webbed, hairs plicate, rarely with additional webs under the marginal veins; lemmas 3.5-5 mm, lanceolate, distinctly keeled, keels and marginal veins sparsely short- to long-villous, margins glabrous, apices acute; palea keels scabrous, glabrous or softly puberulent to long-villous at midlength; anthers vestigial (0.1-0.2 mm) or 1.6-2.7 mm. |
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2n | = 28, 28+11, 56, 56+11, 59, ca. 70. |
= 42, ca. 54, 56, ca. 63, 84. |
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Poa cusickii |
Poa arachnifera |
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Distribution |
CA; CO; ID; MT; ND; NV; OR; UT; WA; WY; AB; BC; MB; SK; YT
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AL; AR; FL; GA; IL; KS; LA; MS; NC; NM; OK; SC; TN; TX
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Discussion | Poa cusickii grows in rich meadows in sagebrush scrub to rocky alpine slopes, from the southwestern Yukon Territory to Manitoba and North Dakota, south to central California and eastern Colorado. It is gynodioecious or dioecious. Sexually reproducing plants of Poa cusickii subspp. cusickii and pallida grow in different geographic areas, but pistillate plants of these two subspecies have overlapping ranges. Only pistillate plants are known in Poa cusickii subspp. epilis and purpurascens. All the alpine plants studied were pistillate. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Poa arachnifera grows on moist, sandy to rich, black bottomlands of the southern Great Plains. At one time it was cultivated for winter pasture in the southeastern United States. It is strictly dioecious, with a 1:1 ratio of staminate to pistillate plants among herbarium samples. The variable and high chromosome numbers suggest it may be apomictic, but the occurrence of equal numbers of staminate and pistillate individuals in populations seems to suggest that reproduction is primarily sexual. It is the only non-South American species in the section. Its closest relatives appear to be P. bonariensis (Lam.) Kunth and P. lanuginosa Poir. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 559. | FNA vol. 24. | ||||||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Madropoa > subsect. Epiles | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Dioicopoa | ||||||||||||
Sibling taxa | ||||||||||||||
Subordinate taxa | ||||||||||||||
Name authority | Vasey | Torr. | ||||||||||||
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