Emergent aquatic, to 1 m high. Mature blade 5–21 cm long; main veins conspicuous, c. 11–20; cross veins inconspicuous, (1–) 1.5–4 mm apart. Inflorescence whorls 3–8 per stem or stem branch. Bracts lanceolate, c. 3 cm long, shorter upwards, maroon. Male flowers on pedicels c. 9–14 mm long, in polygamous whorl, the pedicel 0.4–0.5 mm diam., in male whorls 0.15–0.25 mm diam.; sepals 3, c. 4.2–5 mm long, reflexed; petals 3, c. 6–6.3 mm long; stamens 6, maroon. Bisexual flowers similar to male but carpellate; pedicels 25–60 mm long, 1.5–3.5 mm diam. when in fruit; carpels 3–16, free, c. 3 mm long. Fruiting carpels c. 10–13 mm long, with small ridges bearing 2–5 spines 3–5 mm long, usually also some smaller spines. Seeds 1 per carpel, c. 7 mm long.
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