Tall, rhizomatous perennial. Culms terete, mostly 100–200 cm high, 3–10 mm diam. Leaves reduced, rarely with a blade to 10 cm long. Inflorescence umbel-like, with branches 1–8 cm long, scabrous, with 1–4 spikelets per branch; involucral bract much shorter than inflorescence, 2–5 cm long. Spikelets oblong-ovoid, acute, 5–11 mm long, 4–5 mm diam; glumes recuse, very shortly mucronate, with ciliate margins, red-brown, 3–4 mm long. Hypogynous bristles retrorsely scabrous, slightly longer than or equalling nut; style 2(–3)-fid. Nut obovoid, plano-convex, smooth, shining, grey-brown to dark brown, 2–2.5 mm long, 1.2–1.5 mm diam. Flowers spring–summer.
MuM, Wim, GleP, Brid, VVP, VRiv, MSB, RobP, MuF, GipP, OtP, WaP, Gold, CVU, DunT, NIS, EGL, EGU, WPro, HSF, HNF, OtR, Strz, MonT, HFE. Widespread and locally common in the lowlands, fringing fresh and brackish rivers, lakes and open swamps, bases often submerged.
