Erect, emergent, perennial herb, rooting in substrate, most species monoecious. Submerged leaves strap-shaped, flat or occasionally terete; petiole not developed; emergent leaves with a long slender petiole, expanded and slightly sheathing basally; lamina linear to broadly ovate, or sagittate. Inflorescence erect or with non-flowering part bending, racemose, with flowers arranged in 1 or more successive pseudowhorls which are separated by a long axis; each pseudowhorl of 3 flowers and subtended by 3 partly united bracts; basal pseudowhorls of female flowers; distal pseudowhorls of male flowers. Female flowers with carpels numerous, free, spirally arranged; male flowers with stamens numerous; filaments broad. Aggregate fruit of 1-seeded achenes.
40 species, mainly native of North America; c. 5 naturalised in Australia, 2 or 3 in Victoria.