Submerged, monoecious, slender annual, to 1 m tall. Stems c. 0.5 mm diam.; internodes not spinescent. Leaves linear-lanceolate, flat, 11–22 mm long, 0.32–0.91 mm wide (including spines), acute; margins serrulate with spines on small multicellular excrescences, together (0.04–) 0.06–0.12 (–0.15) mm long; septa and fibres absent; midrib without spines; sheath slightly auriculate; auricle 0.15–0.4 mm long (including spines), serrulate or lacerate, acuminate, with 2–12 spines on each side. Male and female flowers at different nodes, but males more common towards plant apex. Male flowers spatheate, 0.7–0.8 mm long; anther 0.60–0.65 mm long, unisporangiate. Female flowers espatheate, 1.2–2.2 mm long; ovary 0.6–1.6 mm long; style and stigma 0.6 mm long; stigma 2-or 3-lobed. Seed 1.6–1.7 mm long; style base persistent; testa distinctly pitted with areoles regularly arranged in longitudinal rows of 40–50.
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