Tussock-forming perennial, occasionally proliferating, with short thick rhizome. Culms often trigonous above, otherwise terete, smooth, smaller and less robust than in C. vaginatus. Leaves reduced to sheaths, except in juvenile plants. Inflorescence head-like or with 1–3 subsidiary dense, globose clusters on branches to 2 cm long; digitate clusters to 1 cm diam.; involucral bracts very rigid, pungent, 2–4 obvious, shorter than to slightly exceeding inflorescence. Spikelets flattened, numerous per cluster, 3–6 mm long, 2–3 mm wide in side view, 8–20-flowered; rachilla not winged, persistent; glumes with 3-nerved keel but often with 1–2 faint nerves on sides, red-brown, 2–2.7 mm long; stamens 3. Nut trigonous, ellipsoid, yellow- to grey-brown, c. one-half as long as glume, c. 1 mm long, 0.5–0.7 mm diam. Flowers spring–summer.

LoM, MuM, Wim, GleP, VVP, VRiv, MSB, RobP, MuF, GipP, Gold, CVU, DunT, NIS. All mainland states. On banks of streams and lakes.

Cyperus gymnocaulos and C. vaginatus are very closely related and, although each occurs in pure form over considerable areas of Australia, inter-grades are not uncommon in some areas.