Rottboellia longiflora J. D. Hooker, Fl. Brit. India 7: 154. 1896 ["1897"]; R. longiflora var. tonkinensis (A. Camus) A. Camus; R. tonkinensis A. Camus.

Perennial. Culms loosely tufted, erect from decumbent base, 30–80 cm tall, 2–4 mm in diam., glabrous, spongy, nodes usually pubescent. Leaf sheaths loose, sub-compressed, indistinctly keeled; leaf blades linear-lanceolate, 6–15 × 0.5–0.8 cm, slightly flaccid, glabrous, base subcordate; ligule 0.8–2 mm. Racemes solitary or fascicled, 10–15 cm, stout, articulation line oblique, disarticulating tardily. Sessile spikelet twice as long as adjacent internode, 8–15 mm; callus triangular, 0.1–0.6 mm; lower glume lanceolate, back flat, margins scabrid, apex acuminate-caudate to awnlike; upper glume not adnate to rachis, 10–12 mm, acuminate-caudate; lower floret 3–7 mm; upper floret ca. 4 mm, palea very short. Pedicelled spikelet 8–20 mm, lower glume caudate-aristate, upper glume narrowly acuminate. Fl. and fr. Jul–Oct.

Ponds, ditches, other wet places; below 1000 m. Hainan, Yunnan [Bangladesh, NE India, Malaysia, Myanmar, Thailand, Vietnam].