Rottboellia altissima Poiret, Voy. Barbarie 2: 105. 1789; Hemarthria compressa (Linnaeus f.) R. Brown var. altissima (Poiret) Maire; H. compressa var. fasciculata (Hackel) Keng; Rottboellia compressa Linnaeus f. var. fasciculata Hackel; R. fasciculata Lamarck, nom. illeg. superfl.

Perennial, or sometimes annual. Culms loosely tufted to decumbent or stoloniferous, rooting at lower nodes, ascending up to 1.6 m tall, nodes glabrous. Leaf sheaths loose, compressed, keeled, usually shorter than internodes, glabrous except near mouth; leaf blades linear, 5–25 × 0.3–0.6 cm, acute; ligule ca. 0.3 mm. Racemes solitary or several per node, 5–10 cm, semicylindrical, articulation line oblique, tardily disarticulating. Sessile spikelet longer than adjacent internode, 5–7 mm; callus triangular, 0.8–2 mm; lower glume elliptic-oblong, leathery, flat on back, often with subapical constriction, apex obtuse to emarginate; upper glume papery, adnate to rachis, 4–7 mm, apex obtuse to acute; lower floret 3.5–5.2 mm; upper floret 3.2–4.6 mm. Pedicelled spikeletnarrowly lanceolate, lower glume acute, upper glume acuminate. 2n = 20, 36.

Hemarthria altissima occurs naturally mainly from the Mediterranean region through Africa, but there are scattered records from Asia and it is now widely naturalized in warm parts of America.

In or near water, damp places; 700–1900 m. Anhui, Beijing, Guizhou, Heilongjiang, Henan, Hubei, Shandong, Yunnan, Zhejiang [India, Indonesia, Myanmar, Thailand, Vietnam; Africa, SW Asia, Mediterranean region; introduced in America and New Zealand].