Herb, perennial, dioecious, rhizomatous, forming very large tussocks to 60 cm across; cluster roots present. Rhizomes stout, to 20 cm long, 7–10 mm diam.; scales straw-coloured, partly covering a dense white pubescence. Culms spaced c. 2 cm apart, stout, erect, terete to subterete, finely striate, 1.5–2 (–2.5) m long, 7–8 mm diam. near the base, 4.5–5.0 mm diam. mid-culm, internodes 9–12 cm long, fistular, bright green or yellow-green, glabrous above, hoary tomentose basally; upper branches flattened adaxially, concavo-convex; culm branches dimorphic: floriferous branches long, straight; sterile branches short, densely branched into filiform segments with short internodes. Sheaths of culms and fertile branches 2–3 cm long, brown, glabrous or shortly pubescent, apex acute to obtuse; ligule a narrow ridge with dense very short hairs; lamina erect, 4–15 mm long, caducous; sheaths of sterile branches green or tan, auriculate, 2–5 mm long with a linear lamina 5–12 mm long and a tuft of white axillary hairs. Male inflorescences much-branched, to 50 cm long, with very numerous spikelets. Female inflorescence with slender lateral branches 25–45 cm long. Male spathes ovate to elliptic, truncate, 3 mm long with an awn 1–4 mm long. Female spathes lanceolate, rigid, 20–25 mm long with an awn 10–15 mm long. Male spikelets on pedicels to 2 cm long, ovoid or obconical, 7–11 (–25) mm long, 2.5–4 mm wide, with 2–4 sterile lower glumes and c. 30–50 fertile upper glumes; glumes ovate, 3.0–3.7 mm long, light brown, pubescent, apex obtuse to acute; awn erect, terete, 1.8–2.6 mm long. Female spikelets 30–50 mm long, 10–15 mm wide, with 1–3 sterile lower glumes and 1–5 fertile upper glumes; glumes rigid, becoming woody, broadly ovate, c. 1.5 cm long, brown, striate, pilose when young, becoming glabrous, apex aristate; awn erect, c. 1–1.5 cm long. Male flowers: tepals 6, lanceolate, 2.5–3.3 mm long, brown, hyaline; 2 lateral outer tepals keeled; filaments 2.5–2.7 mm long; anthers 2.3 mm long, exserted. Female flowers: tepals apically pubescent; outer tepals rigid, elliptic, 6–10 mm long with an awn c. 10 mm long; inner tepals hyaline, ovate, truncate, 3–6 mm long; staminodes minute; ovary 2-locular; style branches 2, shortly connate at base. Capsule c. 10 mm long, 4–7 mm wide. Seed obloid, furrowed on the abaxial side, 4.2–5.2 mm long, 2–3 mm wide; surface cells slightly convex, lobed, separated from adjoining cells by deep narrow crypts. Culm anatomy: chlorenchyma of 2 or 3 layers of short peg cells, interrupted by pillar cells and partial sclerenchyma ridges opposite outer vascular bundles, central cavity present.
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