21. Poa pratensis Linnaeus, Sp. Pl. 1: 67. 1753.
草地早熟禾 cao di zao shu he
Poa florida N. R. Cui.
Perennials, loosely tufted or with isolated shoots, strongly rhizomatous, often forming turf; shoots extra- and often intravaginal. Plants green to pale or yellowish green, or purplish to strongly grayish glaucous. Culms 10–120 cm, 1–2.5 mm in diam., erect or decumbent, 1 to several per tuft, smooth, nodes (1–)2–4, 1 or 2 exserted. Leaf sheaths moderately compressed and keeled, uppermost closed for (1/4–)1/3–2/5 of length, smooth or infrequently retrorsely scabrid or pilulose; blades flat or folded, papery to thickly papery, 1–5 mm wide, surfaces smooth or sparsely scabrid, margins scabrid, adaxially glabrous or frequently sparsely hispidulous to strigulose, of tillers, flat or folded with margins inrolled, intravaginal ones when present often folded, 0.5–2 mm wide, extravaginal ones flat or folded (1–)1.5–5 mm wide; ligule whitish, 0.5–4(–5) mm, abaxially nearly smooth to densely scabrid, apex truncate to rounded, often finely scabrid to ciliolate or pilulose. Panicle loosely contracted to open, oblong to broadly pyramidal, erect or slightly lax, (2–)5–20(–25) cm, longest internodes 1–4.2 cm; branches steeply ascending to widely spreading, (2–)3–5(–9) per node, rounded or distally angled, nearly smooth to distally scabrid with hooks on and between angles, longest branch 1.5–5(–10) cm with (3–)7–18 spikelets in distal 1/3–2/3, sometimes clustered distally. Spikelets ovate, green or grayish, frequently purple tinged, 3–7(–9) mm, florets 2–5(–9); vivipary absent in China; rachilla internodes 0.5–1(–1.2) mm, smooth, glabrous (rarely sparsely pilulose); glumes subequal, strongly keeled, keels and sometimes lateral veins dorsally scabrid, first glume 1.5–3(–4) mm. 1–3-veined, upper glume 2–4 mm, 3(or 5)-veined; lemmas ovate to lanceolate (or narrowly lanceolate), 2.5–4(–5) mm, apex slightly obtuse to acuminate, keel villous for 3/4 of length, marginal veins to 1/2 length, intermediate veins prominent, glabrous (rarely sparsely pilulose), glabrous between veins, minutely bumpy, sparsely scabrid distally; callus webbed, hairs as long as lemma, frequently with less well-developed tufts from below marginal veins; palea usually narrow, glabrous or with sparse hooks, usually minutely bumpy, glabrous between keels, keels scabrid, infrequently medially pilulose in subsp. pruinosa. Anthers (1.2–)1.4–2.5(–2.8) mm, infrequently poorly formed, but not vestigial. Fl. and fr. Jun–Sep. 2n = 28–144.
Temperate to arctic, moderately moist to wet conditions, from coastal meadows to forest shade, to alpine and tundra, often in disturbed sites; 500–4400 m. Anhui, Gansu, Guizhou, Hebei, Heilongjiang, Henan, Hubei, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Ningxia, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xinjiang, Xizang, Yunnan [Afghanistan, Bhutan, India, Indonesia, Japan, Kazakhstan, Korea, Kyrgyzstan, Mongolia, Myanmar, Nepal, New Guinea, Pakistan, Russia, Sri Lanka, Tajikistan, Turkmenistan, Uzbekistan; Africa, SW Asia, Australia, Europe, North America, Pacific Islands, South America].
Poa pratensis is a valuable species for soil stabilization and forage. Its taxonomy is complicated by the occurrence of facultative apomixis and an extensive polyploid series. It comprises many local and variable, widespread races. It is possible to recognize the widespread forms as subspecies, but there are many intermediates between them that do not fit well and we can only treat them as P. pratensis s.l. The type of P. florida appears to belong to this species, but has many more florets per spikelet (6–9) than is usual.
