Submerged, rhizomatous, aquatic herbs of saline marshes or brackish waters. Roots fibrous. Leaves filiform, linear, alternate or the involucral ones subopposite, with auriculate sheaths at the base. Flowers 2, small, sessile, one above the other, in a terminal spike; spike at first shortly peduncled and covered by the sheaths of the involucral leaves; peduncle more or less elongated and exposed after anthesis. Flowers ebracteate, bisexual. Perianth none. Stamens 2, opposite each other; anthers sessile, or subsessile extrorse, 2-celled, lobes reniform, separated by the connective. Gynoecium of 4 or more superior free carpels; carpels sessile when young, usually becoming stipitate in fruit; stigma sessile, peltate or umbonate. Ovule solitary, pendulous, campylotropous. Fruitlets indehiscent. Seed pendulous, lacking endosperm.