Herbs with milky sap. Leaves sheathing at base; axillary scales present. Inflorescences branched [unbranched], projected above water. Flowers bilaterally symmetric, sessile; stamens 6--18--[50]; filaments distinct; anthers 2-locular; pistils 2--6[--9], sessile. Fruits: beak terminal [lateral], curved or straight. Seeds: endosperm absent; seed coat single or double. x = 8.