Poa annua |
Poa unilateralis |
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annual blue grass |
ocean bluff blue grass, San Francisco bluegrass, sea-bluff bluegrass |
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Habit | Plants usually annual, rarely surviving for a second season; not rhizomatous, sometimes stoloniferous, densely tufted. | Plants perennial; frequently glaucous; densely tufted, not stoloniferous, not rhizomatous. | ||||
Culms | 2-20(45) cm, prostrate to erect, slender; nodes terete, usually 1 exserted. |
5-40 cm, erect or ascending, frequently decumbent, terete, with 0-2 exserted nodes. |
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Sheaths | closed for about 1/3 their length, terete or weakly compressed, smooth; ligules 0.5-3(5) mm, smooth, glabrous, decurrent, obtuse to truncate; blades 1-10 cm long, 1-3(6) mm wide, flat or weakly folded, thin, soft, smooth, margins usually slightly scabrous, apices broadly prow-shaped. |
closed for 1/10(1/5) their length, terete, smooth, glabrous, bases of basal sheaths glabrous, distal sheath lengths 1-4 times widths; ligules 2-6 mm, smooth or sparsely scabrous, obtuse to acute; innovation blades usually 1-1.5 mm wide, thin, soon withering, and distinctly narrower than the cauline blades, infrequently wider, flat, and a bit fleshy as in the cauline blades, or involute; cauline blades gradually reduced in length distally, 2-5 mm wide, flat or folded, soft, thin and soon withering or moderately thick and somewhat fleshy and retaining their form, smooth, apices narrowly to broadly prow-shaped. |
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Basal branching | intravaginal, innovations common, similar to the culms. |
all or mainly intravaginal. |
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Panicles | 1-7(10) cm, lengths 1.2-1.6 times widths, erect; nodes with 1-2(3) branches; branches ascending to spreading or reflexed, straight, terete, smooth, with crowded or loosely arranged spikelets. |
3-7 cm, erect, nearly cylindrical, contracted, congested, with (20)30-80(120) spikelets; nodes with 3-7 branches; branches 0.5-1.5(4.5) cm, erect, usually angled, infrequently terete or sulcate, angles usually moderately to densely scabrous, infrequently smooth with dense papillae and weak-angled, with 2-10 spikelets in the proximal 2/3; pedicels shorter than the spikelets. |
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Spikelets | 3-5 mm, laterally compressed; florets 2-6; rachilla internodes smooth, glabrous, concealed or exposed, distal internodes less than 1/2(3/4) the length of the distal lemma. |
4.5-7 mm, lengths to 3.5 times widths, lanceolate to narrowly ovate, drab; florets 3-5; rachilla internodes usually shorter than 1 mm, smooth. |
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Glumes | smooth, distinctly keeled, keels smooth; lower glumes 1-veined; upper glumes shorter than or subequal to the lowest lemma; calluses glabrous; lemmas 2.5-4 mm, lanceolate, distinctly keeled, smooth throughout, the keels, marginal veins, and, usually, lateral veins crisply puberulent to long-villous, rarely glabrous throughout, lateral veins prominent, intercostal regions glabrous, margins smooth, glabrous, apices obtuse to acute; palea keels smooth, usually short- to long-villous, rarely glabrous; anthers 0.6-1.1 mm, oblong prior to dehiscence, those of the upper 1-2 florets usually vestigial. |
lanceolate, slightly unequal, distinctly keeled, keels papillate or scabrous; lower glumes 3-veined; calluses glabrous or with a crown of hairs, hairs 0.1-0.2 mm; lemmas 3-4.5 mm, lanceolate, distinctly keeled, glabrous or the keels and marginal veins short-villous to midlength, intercostal regions sparsely puberulent near the base, margins glabrous, apices acute; palea keels scabrous, sometimes softly puberulent at midlength; anthers 1.5-3 mm. |
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2n | = 28. |
= 42, 84. |
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Poa annua |
Poa unilateralis |
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Distribution |
AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; HI; PR; AB; BC; MB; NB; NL; NS; NT; ON; PE; QC; SK; YT; Greenland
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CA; OR; WA
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Discussion | Poa annua is one of the world's most widespread weeds. It thrives in anthropomorphic habitats outside of the arctic. A native of Eurasia, it is now well established throughout most of the Flora region. Poa annua is a gynomonoecious tetraploid (possibly rarely polyhaploid), and is thought to have arisen from hybridization between P. infirma (see next) and P. supina (p. 521) (Tutin 1952). It is similar to P. infirma, differing in having larger anthers. It differs from P. chapmaniana (p. 534) in having glabrous calluses and three larger anthers, rather than one. Forms with glabrous lemmas occur sporadically within populations. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Poa unilateralis grows on grassy bluffs and cliffs near the Pacific coast of North America, from Washington to California. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 519. | FNA vol. 24, p. 594. | ||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Micrantherae | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Secundae > subsect. Halophytae | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Synonyms | P. annua var. reptans, P. annua var. aquatica | |||||
Name authority | L. | Scribn. | ||||
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