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FOC | Family List | FOC Vol. 22 | Poaceae | Poa

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.

1 Blades somewhat tough and slightly fleshy, folded, not setiform, 2–5 mm wide, grayish green, sterile shoot leaves usually curved outward; panicle somewhat lax, branches ± smooth; plants from somewhat saline habitats in mountains and steppe basins of C Asia.   21d subsp. pruinosa
+ Blades flat or folded, sometimes setiform, not fleshy, 0.5–4(–5) mm wide, sometimes with a bluish tinge, but not grayish green; sterile shoot leaves mostly straight (sometimes curved in subsp. alpigena)   (2)
2 (1) Lemmas 4–4.5 mm, lower glume 3–4 mm   (3)
+ Lemmas 2.5–3.5(–5) mm, lower glume 2–3.5(–4) mm   (4)
3 (2) Panicle 4–8 cm; branches 2 per node, distally sparsely scabrid, spikelets clustered in distal 1/3, clusters somewhat pendent.   21f subsp. staintonii
+ Panicle 10–15 cm; branches 3–5 per node, distally moderately scabrid, spikelets loosely arranged in distal 1/2, not pendant.   21g subsp. stenachyra
4 (2) Innovations and flowering shoots in small clusters, usually enclosed by dead leaf sheaths; shoots connected by long rhizomes; blades of the innovation leaves usually setiform, convolute, 0.4–1 mm in diam.; plants 20–100 cm tall; panicle usually slightly lax, compressed after anthesis; branches slightly scabrid; lemmas 2.5–3.5 mm; ligule glabrous.   21b subsp. angustifolia
+ Innovation shoots usually solitary, rarely somewhat appressed, but not forming dense clusters   (5)
5 (4) Sheaths of lower leaves somewhat scabrid due to very short hairs; innovation leaf blades usually convolute, moderately firm, 0.4–0.7 mm in diam.; panicle lax, branches scabrid; lemmas 2.8–3.5 mm; culms 30–80 cm tall; forest plants of Heilongjiang basin.   21e subsp. sergievskajae
+ Sheaths of lower leaves glabrous and smooth (rarely pilulose, but then blades broader and flat); panicle branches usually slightly scabrid or smooth; lemmas 2.5–4(–5) mm   (6)
6 (5) Plants 8–30(–50) cm tall, with bluish coating, especially prominent on glumes; blades 1.3–4 mm wide, flat; panicle broad, lax; branches slightly scabrid, 1 or 2(or 3) per node; ligule abaxially pilulose.  

subsp. irrigata (see note under 21c. subsp. pratensis)

+ Plants usually larger, usually without bluish coating; panicle branches usually 3–5 per node at lowest nodes   (7)
7 (6) Panicle branches with scattered spinules, sometimes nearly smooth; leaf blade usually flat; plants often with compact aerial shoots; widespread.   21c subsp. pratensis
+ Panicle branches smooth or nearly so; leaf blade often convolute; plants almost always with solitary shoots; arctic and alpine.   21a subsp. alpigena


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