Perennial with long rhizome. Culms rigid, nodeless or 1-noded, terete to irregularly 4-angled, striate, glabrous, smooth or occasionally finely scabrous near apex, 25–100 cm high, 1.3–2 mm diam. Leaves basal; blade 4-angular (often square) in cross-section (rarely narrowly rhomboid), faces often concave, scabrous to smooth, shorter and broader than culm, to 3 mm diam.; sheath pale brown, usually with reddish tinges, dull. Inflorescence ovate in outline, erect, mostly 7–15 cm long, 2–3 cm diam.; lowest involucral bract much shorter than inflorescence. Spikelets numerous, 1-flowered, 3.5–4.0 mm long; glumes 3–5, acute to long-acute, mucronate, ± excurved, very dark red-brown, margins ciliate; fertile glumes c. 4 mm long. Nut obovoid to ellipsoid, with longitudinal and short incomplete transverse ridges, faintly white-papillose between ridges, minutely hispid or papillose at apex, dull, pale brown, 1.8–2.6 mm long, 0.9–1.3 mm diam. Flowers spring–summer.
LoM, Wim, GleP, VVP, GipP, OtP, WaP, Gold, CVU, GGr, DunT, EGL, EGU, WPro, HSF, HNF, OtR, Strz, VAlp. Also SA, Qld, NSW, Tas. Locally common along lowland streams and in swamps fringing heathland or heathy woodland. Sometimes occurring with M. rubiginosa.
