Physkium Loureiro.

Herbs, submerged, stoloniferous, without erect stems. Leaves basal, sessile, linear or strap-shaped, veins 3-9, parallel, slightly sheathed at base, margin minutely serrulate or entire. Plants dioecious; flowers unisexual. Male flowers numerous, minute, shortly pedicellate, clustered together on a central column enclosed by a common spathe, each flower finally breaking free and floating on water surface; spathe ovate or broadly lanceolate, shortly pedunculate; sepals 3, convex, 2 larger than other; petals 2 or 3, minute; stamens 1-3. Female flowers solitary in spathe; spathe tubular, bifid at apex, pedunculate; peduncles long, coiled after anthesis; sepals 3; petals 3, minute; ovary narrowly cylindric or narrowly triangular-cylindric; ovules numerous; styles 3, bifid. Fruit cylindric or triangular-cylindric. Seeds numerous, oblong or fusiform.

About eight species: tropical and subtropical regions; three species (one endemic) in China.