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Poa helmsii

Description

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Family Poaceae

Annual or perennial herbs, or tall woody bamboos . Flowering stems (culms ) jointed , internodes hollow or solid; branches arising singly from nodes and subtended by a leaf sheath and 2-keeled prophyll, often fascicled in bamboos. Leaves arranged alternately in 2 ranks , differentiated into sheath, blade , and an adaxial erect appendage at sheath/blade junction (ligule) ; leaf sheath surrounding and supporting culm-internode, split to base or infrequently tubular with partially or completely fused margins , modified with reduced blade in bamboos (culm sheaths) ; leaf blades divergent, usually long, narrow and flat, but varying from inrolled and filiform to ovate , veins parallel, sometimes with cross-connecting veinlets (especially in bamboos) ; ligule membranous or a line of hairs . Inflorescence terminal or axillary , an open, contracted , or spikelike panicle, or composed of lax to spikelike racemes arranged along an elongate central axis, or digitate, paired , or occasionally solitary; axillary inflorescences often many, subtended by spatheoles (specialized bladeless leaf sheaths) and gathered into a leafy compound panicle; spikelets often aggregated into complex clusters in bamboos. Spikelets composed of distichous bracts arranged along a slender axis (rachilla) ; typically 2 lowest bracts (glumes ) empty, subtending 1 to many florets ; glumes often poorly differentiated from accompanying bracts in bamboos. Florets composed of 2 opposing bracts enclosing a single small flower, outer bract (lemma) clasping the more delicate, usually 2-keeled inner bract (palea) ; base of floret often with thickened prolongation articulated with rachilla (callus) ; lemma often with apical or dorsal bristle (awn ), glumes also sometimes awned . Flowers bisexual or unisexual ; lodicules (small scales representing perianth) 2, rarely 3 or absent, 3 to many in bamboos, hyaline or fleshy ; stamens 3 rarely 1, 2, 6, or more in some bamboos, hypogynous, filaments capillary , anthers versatile; ovary 1-celled, styles (1 or) 2(rarely 3), free or united at base, topped by feathery stigmas, exserted from sides or apex of floret. Fruit normally a dry indehiscent caryopsis with thin pericarp firmly adherent to seed, pericarp rarely free, fleshy in some bamboos; embryo small or large; hilum punctate to linear .

About 700 genera and 11,000 species: widely distributed in all regions of the world.[1]

Genus Poa

Annuals or perennials . Culm bases infrequently swollen, or with bulbous sheath bases; new shoots intravaginal or extravaginal , rarely (in China) pseudointravaginal, intravaginal but with reduced or rudimentary lower leaf blades and weakly differentiated prophyl. Uppermost culm leaf sheath closed from 1/20th to entire length ; ligule hyaline , membranous or infrequently papery ; blade flat, folded, or involute , abaxially keeled , adaxially with 1 groove on either side of the midvein , apex prow-tipped. Inflorescence a terminal panicle; branches 1-9 per node; flowers all bisexual , or mixed bisexual and female (rarely male), with distal female flowers within spikelets , or with partially to wholly female spikelets or inflorescences. Spikelets laterally compressed , florets (1-) 2-8(-10), rachilla disarticulating above glumes and between florets, uppermost floret vestigial; vivipary sometimes present; glumes mostly strongly keeled, unequal, or subequal , lower glume 1- or 3-veined, upper glume 3(or 5) -veined; lemmas laterally compressed, usually distinctly keeled, 5(-7) -veined, distal margins and apex membranous, apex awnless, rarely minutely mucronate ; floret callus short, truncate , blunt , glabrous or webbed (with a dorsal tuft of woolly hairs ), rarely with a line of hairs around base of lemma; palea subequal or infrequently to 2/3 as long as lemma, not gaping , keels green, distinctly separated, usually scabrid , smooth in Poa sect. Micrantherae, sometimes pilulose to villous , margins usually smooth, glabrous. Lodicules 2. Stamens 3, anthers sometimes vestigial. Ovary glabrous. Caryopsis oblong to fusiform , triangular to oval in cross section , sometimes grooved , free or adhering to the palea. 2n = 14-266. x = 7.

More than 500 species: throughout Arctic and N and S temperate regions and extending to most subtropical and tropical mountains, in habitats such as temperate forests, mountain slopes , grasslands, wetlands, steppes , alpine areas and tundra , deserts, and around human habitation, on acidic to sub-basic or subsaline, dry to wet soils, from sea level to the upper limits of vegetation; 81 species (14 endemic, at least one introduced ) in China.

Poa includes many species useful and important for forage , soil stabilization, and lawns, and several widespread weeds . Five of six recognized subgenera are present in China. (1) Poa subg. Arctopoa: stout plants with thick rhizomes, scabrid to ciliate lemma margins, and glabrous calluses, found in subsaline to subalkaline wetlands. (2) Poa subg. Ochlopoa: plants with bulbous sheathed culm bases (spikelets then often viviparous), or if not bulbous then commonly quite smooth throughout, with shortly villous palea keels and no callus hairs, sometimes annuals. (3) Poa subg. Pseudopoa: slender annuals with scabrid-angled panicle branches, shortish glumes, uppermost culm sheaths closed for 1/15-1/10 their length, glabrous calluses, and scabrid rachillas. (4) Poa subg. Poa: the largest and most diverse subgenus , including annuals and perennials, with or without rhizomes, but generally with the uppermost culm sheaths closed for over 1/4 their length. (5) Poa subg. Stenopoa: commonly tufted perennials generally with the uppermost culm sheaths closed for only 1/15-1/5(-1/4) their length, with mainly extravaginal shoots, mostly without rhizomes, mostly with panicle branches that are scabrid angled from the base, and with 3-veined first glumes.

Some species have races with florets that develop into bulbils that can readily send down roots as soon as they drop from the inflorescence (i.e. , they are viviparous). Viviparous spikelets often have fairly normal-looking proximal florets. Pubescence on the lemmas and calluses of such florets is often poorly developed relative to that in normal spikelets, or absent. Identification is easiest with plants having normal spikelets.

Hybridization and facultative apomixis are common in some subgenera, especially Poa subg. Poa and P. subg. Stenopoa, and the vast majority of species studied are polyploid.[2]

Habitat

Typically found at an altitude of 0 to 1,397 meters (0 to 4,583 feet).[3]

Taxonomy

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Similar Species

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Members of the genus Poa

ZipcodeZoo has pages for 1626 species, subspecies, varieties, forms, and cultivars in this genus. Here are just 100 of them:

P. abbreviata (Northern Bluegrass) · P. abietina · P. abortiva · P. abyssinica · P. achrochaeta · P. acicularifolia · P. acicularis · P. acinaciphylla · P. acmocalyx · P. acrochaeta · P. acroleuca · P. acroleuca var. ryukyuensis · P. acuminata · P. acuticaulis · P. acutiflora · P. acutifolia · P. acutiglumis · P. acutissima · P. adjarica · P. adspersa · P. adusta · P. aegyptiaca · P. aemensis · P. aequatoriensis · P. aequigluma · P. aestivalis · P. affinis · P. afghanica · P. agassizensis · P. agrostidea · P. airoides · P. aitchisonii · P. akmanii · P. aksuensis · P. alascana · P. alata · P. alba · P. alberti · P. albescens · P. albida · P. alcea · P. alexeenkoi · P. alexeji · P. algida · P. almasovii · P. alopecurioides 'Woodside' · P. alopecurus · P. alopecurus alopecurus · P. alopecurus subsp · P. alpicola · P. alpigena · P. alpina (Alpine Meadow Grass) · P. alpina f. vivipara (Alpine Bluegrass) · P. alpina minor · P. alpina nodosa · P. alpina alpina · P. alpina var. bivonae · P. alpina var. brevifolia · P. alpina var. minor · P. alpina var. purpurascens · P. alpina vivipara · P. alsodes (Grove Bluegrass) · P. alta · P. altaica · P. alternans · P. altissima · P. altoperuana · P. amabilis · P. ambigua · P. amboinensis · P. amboinicia · P. ammophila · P. amoena · P. ampla · P. amplexicaulis · P. anadyrica · P. anae · P. anceps · P. anceps condensata · P. andicola · P. andina · P. andina spicata · P. andina var. major · P. androgyna · P. anfamensis · P. angusta · P. angustata · P. angustifolia · P. angustifolia var. angustiglumis · P. angustiglumis · P. ankaratrensis · P. annua (Annual Meadow-Grass) · P. annua f. purpurea · P. annua f. reptans (Creeping Bluegrass) · P. annua pilantha · P. annua reptans · P. annua rigidiuscula · P. annua var. nepalensis · P. annua var. rigidiuscula · P. annua var. stricta

More Info

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Further Reading

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Notes

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Contributors

Data Sources

Accessed through GBIF Data Portal December 05, 2007:

Identifiers

Footnotes

  1. Shou-liang Chen, De-Zhu Li, Guanghua Zhu, Zhenlan Wu, Sheng-lian Lu, Liang Liu, Zheng-ping Wang, Bi-xing Sun, Zheng-de Zhu, Nianhe Xia, Liang-zhi Jia, Zhenhua Guo, Wenli Chen, Xiang Chen, Yang Guangyao, Sylvia M. Phillips, Chris Stapleton, Robert J. Soreng, Susan G. Aiken, Nikolai N. Tzvelev, Paul M. Peterson, Stephen A. Renvoize, Marina V. Olonova & Klaus Ammann "Poaceae". in Flora of China Vol. 22. Published by Science Press (Beijing) and Missouri Botanical Garden Press. Online at EFloras.org. [back]
  2. Guanghua Zhu, Liang Liu, Robert J. Soreng & Marina V. Olonova "Poa". in Flora of China Vol. 22 Page 1, 225, 257, 312, 315. Published by Science Press (Beijing) and Missouri Botanical Garden Press. Online at EFloras.org. [back]
  3. Mean = 641.660 meters (2,105.184 feet), Standard Deviation = 383.340 based on 176 observations. Altitude information for each observation from British Oceanographic Data Centre. [back]
Last Revised: 2009-07-04