Submerged aquatic herb. Stems up to 3m long and 2 mm in diameter, longitudinally grooved. Leaves in whorls of 7-11, 8-40 mm long, filiform, forked 1-2(3) times; margin with spine-tipped teeth, particularly in the apical segments. Flowers axillary, unisexual on the same plant; male flowers in many 1-3-flowered clusters per branch; female flowers solitary, few per branch. Fruit ovoid, ellipsoid to obovoid with an apical spine and 2 prominent basal spines, and raised dark spots on the surface.