Description from Flora of China
Herbs, submerged. Stems elongated, slender, much branched. Leaves alternate but usually opposite at base, densely crowded toward ends of stems, linear, lacking a prominent midvein, parallel veins present, slightly sheathing at base, margin minutely serrulate with teeth. Plants dioecious; flowers unisexual. Male inflorescence pedunculate, many flowered; spathe ovate, membranous, bifid at apex; male flowers minute; sepals 3, petaloid, white, ovate; petals 3, small, subequal to sepals; stamens 2 or 3, opposite to sepals; filaments slender, very short. Female spathe oblong, 1-flowered; female flowers similar to male ones; ovary oblong, elongated into a beak at apex; styles 3. Fruit ovoid-oblong or linear. Seeds numerous, oblong, minute.
One species: S and SE Asia.