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FOC | Family List | FOC Vol. 22 | Poaceae

66. Poa Linnaeus, Sp. Pl. 1: 67. 1753.

早熟禾属 zao shu he shu

Authors: Guanghua Zhu, Liang Liu, Robert J. Soreng & Marina V. Olonova

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.

1 Lemma margins scabrid to long ciliate, or at least between lower margin and marginal vein; glumes often ciliolate on lower margins; plants robust with long thick rhizomes; butts of some old basal sheaths retrorsely strigose, hairs 0.1–0.2 mm.   1 P. subg. Arctopoa (species nos. 1–3)
+ Lemma margins smooth or sparsely scabrid; glumes never ciliolate on margins; rhizomes present or absent; butts of old basal sheaths glabrous, infrequently finely strigose in P. subg. Stenopoa, hairs to 0.05 mm   (2)
2 (1) Culms with bulbous bases due to basally swollen sheaths; spikelets frequently viviparous.   2 P. subg. Ochlopoa (P. sect. Arenariae: species nos. 5–7)
+ Culms without basally swollen sheaths (rarely culm base swollen); spikelets infrequently viviparous   (3)
3 (2) Palea keels smooth, pubescent; panicle branches smooth.   2 P. subg. Ochlopoa (P. sect. Micrantherae: species nos. 8–11)
+ Palea keels usually scabrid, glabrous or pubescent, if smooth then panicle branches scabrid; if pubescent then with 1 or more hooks near apex   (4)
4 (3) Panicle branches in distinct whorls; annuals; lower glume 1-veined, much shorter than adjacent lemma.   3 P. subg. Pseudopoa (species no. 12)
+ Panicle branches not clearly whorled; perennials or infrequently annual; lower glume 1- or 3-veined, subequal to or longer than adjacent lemma   (5)
5 (4) Uppermost culm sheath closed for less than 1/4 of length; shoots extravaginal; rhizomes usually absent; panicle branches scabrid; lower glume 3-veined.   5 P. subg. Stenopoa (species nos. 64, 66–81)
+ Uppermost culm sheath closed for ca. 1/4 of length to near top; shoots intravaginal and/or extravaginal; rhizomes sometimes present; panicle branches smooth or scabrid; lower glume 1- or 3-veined   (6)
6 (5) Leaf blades 1–4 mm wide, mostly shorter than 10 cm; lemmas densely villous on keel and marginal veins, appressed short villous between veins; palea keels shortly villous; plant less than 40 cm, forming dense tufts; callus web absent in Chinese species.   2 P. subg. Ochlopoa (P. sect. Alpinae: species no. 4)
+ Leaf blades 1–10 mm wide, some often over 10 cm; lemmas glabrous or pubescent; palea keels glabrous or pubescent; plant up to 120 cm, forming loose or dense tufts; callus web present or absent   (7)
7 (6) Palea keels with minute, smooth to apiculate bumps, without distinctly hooked prickle hairs, glabrous; lemmas pubescent on keel, otherwise glabrous; callus long webbed; ligule acuminate; lower glume 1-veined, often sickle-shaped.   5 P. subg. Stenopoa (P. sect. Pandemos: species no. 65)
+ Palea keels with hooked prickle hairs, glabrous or pubescent between keels; lemmas glabrous or variously pubescent; callus webbed or not; ligule truncate to acuminate; lower glume 1- or 3-veined, usually not sickle-shaped.   4 P. subg. Poa (species nos. 13–63)

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