Herbs, aquatic, with aerial leaves. Leaves petiolate, ovate to orbicular. Scapes erect; umbels terminal; bracts forming an involucre. Pedicels thick. Sepals persistent, green. Petals yellowish, thin. Stamens numerous, with sterile staminodes in outermost whorl; filaments flattened. Carpels numerous, free, crowded into a head, laterally compressed; stigmas sessile. Seeds numerous, strongly curved; embryo horseshoe-shaped.
Flowers in umbelliformous, peduncled inflorescences. Stamens ∞, surrounded by a whorl of staminodes. Ovaries ∞, strongly laterally compressed, free, densely set, seemingly forming one ovary. Stigmas sessile, lineate. Fruitlets semi-circular, in a head, dorsal wall thick. Seeds ∞, small, horse-shoe shaped; testa spongy.