General description:- Submerged or floating aquatic herbs, sometimes marine.
Leaves:- Alternate, opposite or verticillate, sheathing at the base or with nodal scales.
Flowers:- Hermaphrodite or unisexual, 1 or more together in spathes composed of 1 or 2 free or united (connate) bracts. Sepals 3. Petals 3 or 0. Stamens 2-15, free or connate at the base, occasionally some staminodal; filaments elongated or absent; anthers 2-thecous, opening by longitudinal slits. Ovary syncarpous, inferior, often attenuated into a filiform beak. ovules on parietal, sometimes intruded placentas; styles 3-15
Fruit:- Dehiscing irregularly or splitting stellately into valves; seeds without endosperm; embryo straight.
NAJAS
General description:- Monoecious or dioecious.
Leaves:- Conspicuously or minutely dentate at the margins; sheath with or without auricles.
Flowers:- Solitary or few together, ebracteate or with a spathe-like bract, pedunculate or subsessile. Style 2- to 4-branched.
Sect. NAJAS
General description:- Dioecious.
Stems:- Spinose-dentate or smooth.