Poa annua |
Poa occidentalis |
|
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annual blue grass |
New Mexican bluegrass, New Mexico bluegrass |
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Habit | Plants usually annual, rarely surviving for a second season; not rhizomatous, sometimes stoloniferous, densely tufted. | Plants perennial, short-lived; densely tufted, tuft bases narrow or not, not rhizomatous, not stoloniferous. |
Culms | 2-20(45) cm, prostrate to erect, slender; nodes terete, usually 1 exserted. |
20-110 cm. |
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 (1/5)1/4 – 1/2(3/5) their length, distinctly compressed and keeled, usually densely retrorsely scabrous, rarely sparsely scabrous, margins not ciliate; ligules 3-12 mm, densely scabrous, acute to acuminate; blades (1.2)1.5-6(10) mm wide, flat, lax, apices broadly prow-shaped. |
Basal branching | intravaginal, innovations common, similar to the culms. |
mixed intra- and extra-vaginal. |
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. |
(6)12-40 cm, lax, eventually open, spikelets numerous, with 2-7 branches per node; branches (3)5-18(23) cm, eventually spreading or drooping, angled, angles densely scabrous, with (5)8-40(120) spikelets. |
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. |
(3)4-7(8) mm, laterally compressed, with 3-7 florets; rachilla internodes shorter than 1 mm, smooth. |
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. |
distinctly keeled, keels scabrous; lower glumes 2-3.5 mm, 1-veined; upper glumes 2.5-4.2 mm, shorter than or subequal to the lowest lemmas; calluses webbed; lemmas 2.6-4.2 mm, narrowly lanceolate, distinctly keeled, scabrous distally, keels and marginal veins short- to long-villous, keel hairs extending to midlength, marginal vein hairs to 1/3 the lemma length, lateral veins and intercostal regions usually sparsely softly puberulent, lateral veins prominent, apices narrowly acute; palea keels scabrous, glabrous; anthers 0.3-1 mm. |
2n | = 28. |
= 14, 28. |
Poa annua |
Poa occidentalis |
|
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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AZ; CO; NM; TX |
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 occidentalis grows in natural openings and disturbed sites in mixed coniferous forests of the southwestern United States. It is one of the three diploid species of Poa known to be native to North America. The tetraploid count was obtained from a single giant individual. Poa occidentalis has been confused with P. tracyi (p. 543), but P. occidentalis consistently has shorter, well-developed anthers and lacks rhizomes. It also usually has longer ligules relative to the blade width, and is shorter-lived. A few plants are intermediate in some characteristics. Small plants of P. occidentalis sometimes resemble P. reflexa (see next). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 24, p. 519. | FNA vol. 24, p. 536. |
Parent taxa | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Micrantherae | Poaceae > subfam. Pooideae > tribe Poeae > Poa > subg. Poa > sect. Homalopoa |
Sibling taxa | ||
Synonyms | P. annua var. reptans, P. annua var. aquatica | |
Name authority | L. | Vasey |
Web links |
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