Description from Flora of China
Oplismenus cruspavonis Kunth, Nov. Gen. Sp. (quarto ed.) 1: 108. 1815 ["1816"]; Echinochloa crusgalli (Linnaeus) P. Beauvois var. cruspa-vonis (Kunth) Hitchcock; Panicum cruspavonis (Kunth) Nees.
Perennial or rarely annual. Culms robust, usually decumbent at base and forming a large clump, 1.2–1.8 m tall. Leaf sheaths loose, smooth and glabrous; leaf blades linear, lush, 10–40 × 1–1.5 cm, glabrous, midrib broad and white, margins harshly scabrous. Inflorescence nodding, large, loose, 15–25 cm; branches mostly compound, spikelets many, crowded on secondary branchlets. Spikelets purple-tinged, ovate-lanceolate, 2–3 mm, hispid on veins, the hairs not tubercle-based; lower glume 1/3–2/5 as long as spikelet; upper glume rostrate; lower lemma sterile, herbaceous, 5–7-veined, with a stout, 1–1.5 cm awn; upper lemma 2–2.5 mm. Fl. and fr. summer–autumn. 2n = 36, 54.
This is a segregate from Echinochloa crusgalli with a larger, more branched inflorescence and smaller spikelets.
Streamsides and other damp places. Anhui, Fujian, Guangdong, Guizhou, Hainan, Shaanxi, Sichuan [throughout the tropics].