Culms suberect or apically slightly drooping, 1–7 m, (0.3–) 1.5–2.5 cm in diam.; internodes 30–50 cm, thinly white powdery, distally stiffly deciduously brown or dull brown hairy, especially densely so below nodes; wall usually rather thin, solid in var. riviereorum; nodes slightly prominent, glabrous; branching from 2nd or 3rd node up. Branches several to many, clustered, subequal or central slightly dominant. Culm sheaths deciduous, trapezoid, initially thinly white powdery, glabrous, asymmetrically arched, apex slanted along outer side; auricles very small to inconspicuous, oral setae few; ligule 1–1.5 mm, irregularly dentate; blade deciduous, erect, narrowly triangular, base nearly as wide as sheath apex, abaxially with scattered, stiff, dull brown hairs, adaxially scabrous, apex acuminate. Leaves 5–26 per ultimate branch; leaf blade abaxially pale glaucous, adaxially bright green, linear, 1.6–16 × 0.3–1.6 cm, abaxially densely pubescent, adaxially glabrous. Pseudospikelets solitary or several clustered at nodes of flowering branches, linear to linear-lanceolate, 3–6 cm; prophylls ca. 3.5 mm, 2-keeled, keels ciliolate; gemmiferous bracts usually 1 or 2, ovate to narrowly ovate, 4–7.5 mm, glabrous, 9–13-veined, apex obtuse or acute; florets (3–)5–13, middle ones fertile; rachilla segments flat, 4–4.5 mm, glabrous. Glumes absent; lemma asymmetrical, oblong-lanceolate, ca. 1.8 cm, glabrous, 19–21-veined, apex acute; palea linear, 1.4–1.6 cm, keels ciliolate, 6-veined between and 4-veined on one side and 3-veined on other side of keels, apex subtruncate, ciliolate, with a fine hairy tip on each side; lodicules 3, anterior 2 subovate, 2.5–3 mm, posterior narrowly lanceolate, 3–5 mm, margins glabrous. Filaments 0.8–1 cm; anthers purple, ca. 6 mm, apex penicillate. Ovary ovoid, ca. 1 mm, base with stalk ca. 1 mm, apex thickened and hispidulous; stigmas 3 or variable in number, ca. 5 mm, directly exserted from ovary apex. Mature caryopsis unknown.