Basal leaves erect, 70–160 cm long, 8–17 mm wide. Inflorescence 4–6-branched, the terminal branch as long as or slightly longer than the basal branches. Female heads 1–2(–3) per branch; each basal head distant from the axil of a leaf-like bract or subtended by a very reduced bract; distal heads rarely subtended by a leaf-like bract. Male heads 7–13 per branch. Fruiting heads (15–)20–25 mm wide. Flowers Nov.–May.
VVP, VRiv, GipP, WaP, NIS, EGL. Forms dense populations in still or slowly flowing freshwater.
Australian occurrences of this Northern Hemisphere plant were formerly regarded as native, but the rapid expansion in its range in recent years suggests it has become naturalised since its pre-1900 introduction.
