Submerged marine perennials with creeping rhizomes. Stems flattened, slender, simple or branched. Leaves in two rows, linear, sheathing at base. Plants monoecious or dioecious, the flowers arranged on 1 side of a flattened axis or spadix, at first enclosed in the leaf sheath; bracts lacking. Perianth absent or represented by a row of branchlike lobes on each side of the axis. Staminate flowers reduced to a single anther, arranged alternately in 2 rows on the spadix. Pistillate flower an ovary with 2 stigmas and 1 ovule. Fruit indehiscent or bursting irregularly. Seed without endosperm.
Family or 2 widely distributed genera. (Munz, Flora So. Calif. 1013).