Tufted annual or short-lived perennial. Culms filiform, to 12 cm high. Leaves reduced, blade to 7 mm long. Spikelets 1–4 per inflorescence, 2.5–5.5 mm long; Involucral bract shorter than to slightly exceeding inflorescence; glumes acute, mucronate, sides 2–3 nerved, usually dark brown, 1.2–1.9 mm long; stamens 2–3; style 3-fid, rarely 2-fid (not in Victoria). Nut terete, globose, reticulate, tuberculate, yellowish-brown to brown, about half as long as glume, 0.7–0.9 mm long, 0.5–0.6 mm wide. Flowers Spring–Summer.
VRiv, GipP, Gold. Also SA (treated as introduced). South Africa (endemic to Cape Peninsula). In Victoria, the species is known from several relatively recently collected specimens from the Bendigo region, with an isolated record from Frankston. Plants are generally found growing in disturbed wet depressions.
Isolepis trachysperma superficially resembles I. hookeriana from which it is distinguished by darker coloured glumes and the nut which is lighter coloured, tuberculate, with diamond-shaped reticulate patterning (cf. striate and trabeculate in I. hookeriana).
