Small or minute annual to perennial aquatic thalloid floating or submerged fresh water herbs. Fronds small or grain like, simple, symmetrical or asymmetrical, flat, curved or suborbicular; stem and leaves undifferentiated. Root simple, 1-many on ventral surface of fronds or absent; root hairs absent. Plants monoecious; inflorescence minute; developing in a pouch or pit, enclosed by spathe or without spathe. Staminate flowers 2 or 1, anthers 4 or 2-thecous, pistillate flowers solitary; style very short; stigma concave. Placentation basal, 1-6 ovules. Fruits ribbed or ± smooth and ellipsoid. Flowering erratic. Re-production usually vegetative; daughter fronds budding from a lateral pocket or terminal pit, often remaining attached to the parents. Turions (resting buds) sometimes produced in adverse conditions.