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Submerged rootless aquatic perennial herb. Stems branched, with whorled leaves, up to 1 m long. Terrestrial form not known. Leaves dark green, rigid, 1–2 times forked and toothed. Flowers monoecious, subaquatic, sessile, solitary in leaf axils. Fruit is an achene, apiculate to long-spined at apex, often with 2 long spines at base. Overwinters in apical, loose cone-shaped turions.