70. Poa palustris Linnaeus, Syst. Nat., ed. 10. 2: 874. 1759.
泽地早熟禾 ze di zao shu he
Culms loosely tufted, 40–80(–120) cm tall, erect or slightly geniculate, rarely branching near base; nodes 5 or 6, uppermost at or above middle of culm. Shoots extravaginal. Leaf sheath smooth or rarely scabrid; equal to or shorter than blade; blade flat, 8–20 cm × 2–3(–5) mm; ligule 2–3 mm. Panicle slightly contracted, 10–20(–30) cm; branches obliquely ascending, 3–8 per node, basal primary branch 1/2–2/3 as long as panicle with spikelets in distal 1/2. Spikelets ovate-oblong, yellowish green, 2.5–5(–7) mm, florets (2–)3–5(–7); rachilla scabrid or warty, rarely smooth; glumes almost equal, 2–3.5(–4) mm; lemma 3–3.5(–4) mm, keel shortly villous for 1/2 of length, marginal veins for 1/3, apex golden or rarely silvery, membranous; callus webbed; palea keel scabrid, area between keels smooth and glabrous. Anthers 1.2–1.5(–2) mm. Fl. Jun–Jul. 2n = 28, 30, 32, 42.
Meadows among scattered thickets on slopes, marshy grasslands; 300–3500 m. Anhui, Hebei, Heilongjiang, Henan, Nei Mongol, Xinjiang [India, Japan, Kazakhstan, Korea, Kyrgyzstan, Mongolia, Pakistan, Russia, Tajikistan; SW Asia, Europe, North America].
Poa palustris, like P. nemoralis, is one of the most complicated and polymorphic species. Hybridization with P. nemoralis, coupled with apomixis, has formed a series of morphologically and genetically distinct populations treated here as P. lapponica.
Despite its great polymorphism, Poa palustris has not been divided satisfactorily into stable taxa. Its distribution in China seems to be quite restricted, limited to the northern regions only. It is probably naturalized in central and southern areas. In the mountains of the south and southwest it is replaced by the allied species P. faberi. In E China, Japan, and Korea it is very close to, and probably replaced by, a third, related species, P. sphondylodes. Unusual plants in Anhui differ by the glumes and lemma being much narrower with a prominent vein. Some populations of P. palustris in N China and even in the Russian Far East differ from normal P. palustris by the appearance of characters of P. sphondylodes: ligule longer than 3–4 mm, upper node infrequently only to 1/3 way up culm, leaf blades soft and flat, panicle branches sometimes very short, spikelets crowded at very base of branches, and longest branches at 2nd node of panicle. Both Ohwi (Fl. Jap. 164. 1965) and Koyama (Grasses Japan Neighboring Regions, 96. 1987) reported P. palustris with a ligule to 5 mm from Japan; similarly Chung (Korean Grass. 71. 1965) and Lee (Man. Korean Grass. 154. 1966) from Korea. Poa palustris with such long ligules occurs in the Pacific area only, and these plants might be closer to P. sphondylodes. Such plants may also be found in coastal areas of China.