Perennial aquatic herb. Rhizome woody, fibre-covered, 6–12 mm thick. Tubers globularobloid, 4–13 (–17) mm long, 3–6 mm diam.; terminating short roots 1–7 (–14) mm long, rarely elongate on longer roots. Leaves ± linear, usually erect, to 137 cm long and 12 mm wide, thickly spongy basally; basal sheaths tapered; T.S. c. 3 cm below sheath summit ± semicylindric, with width of spongy portion only 1.6–2.4 times its thickness and with sheath margins incurved, usually touching to overlapping. Scape at fruiting c. 47–103 cm long, 2.5–12.6 mm diam. Infructescence a raceme, 7–21 cm long, 15–24 mm diam.; pedicels 0.5–3 mm long. Fruits c. 44–137 per infructescence, touching, very broadly obovoid with a squat summit and contracted, stalk-like base, 7–9.6 mm long, 5.5–8.2 mm diam. Carpels (5 or) 6, normally all maturing; central axis absent; mature carpels attached along 58%–70% of length, never twisted, ± triangular in T.S. with dorsal surface flat or shallowly indented, rarely shallowly convex.
Grows in fresh, still or slow-flowing water to 50 (–120) cm deep, in small creeks, swamps and farm dams, on silt, peat, loam or sand soils. Stagnant water often highly eutrophic and humic from farmland runoff. Alt. c. 3–100 (–400) m.
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