5. Hemarthria compressa (Linnaeus f.) R. Brown, Prodr. 207. 1810.
扁穗牛鞭草 bian sui niu bian cao
Rottboellia compressa Linnaeus f., Suppl. Pl. 114. 1782 ["1781"]; Hemarthria coromandelina Steudel, nom. illeg. superfl.; H. glabra (Roxburgh) Blatter & McCann; H. laxa Nees ex Steudel; Manisuris compressa (Linnaeus f.) Kuntze; Rottboellia glabra Roxburgh.
Perennial. Culms decumbent to long-stoloniferous, rooting at lower nodes, up to 1 m or more, much branched from base, nodes conspicuous, dark, glabrous. Leaf sheaths loose, compressed, keeled, glabrous or hairy along mouth, often shorter than internodes; leaf blades linear, 2–15 × 0.2–0.5 cm, base rounded, apex subacute; ligule 0.3–1 mm. Racemes solitary or few per node, lightly compressed, 2–10 cm, articulation line oblique, tardily disarticulating. Sessile spikelet slightly longer than adjacent internode, 3–5 mm; callus broadly triangular, 0.5–1 mm; lower glume narrowly oblong, leathery, flat or subconvex on back, abruptly constricted into obtuse or emarginate apex; upper glume adnate to rachis, equaling lower glume, thin, acute; lower floret 2.4–3.3 mm; upper floret 2–3.2 mm, palea small, rarely absent. Pedicelled spikelet 2.4–5 mm, lower glume narrowly obtuse, upper glume acuminate-caudate. Fl. and fr. Jul–Sep. 2n = 18, 27, 36.
Marshes, wet places, coasts; below 2000 m. Fujian, Guangdong, Guangxi, Guizhou, Hainan, Nei Mongol, Shaanxi, Sichuan, Taiwan, Yunnan [Afghanistan, Bangladesh, Bhutan, India, Japan, Laos, Malaysia, Myanmar, Nepal, Pakistan, Sri Lanka, Thailand, Vietnam; SW Asia (Iraq)].
Hemarthria compressa is not completely distinct from H. altis-sima, but is generally a more slender plant with smaller spikelets.