small to minute, aquatic, floating or submerged, mostly perennial plants,
reduced to small green bodies called fronds, corresponding partly to leaf and
partly to stem. Roots absent or reduced to unbranched rhizoids. Fronds 1-many,
coherent together, orbicular or oblong to lanceolate, 0.4-15 mm long, reproducing mostly by budding of daughter fronds
from reproductive pouch or cavity. Flowers rare, 1 (or 2) from one of
pouches, monoecious, perianth absent.
Male flowers : stamens 1-2, filaments
slender, anthers 1-2 locular. Female flowers : ovary 1, tapering into style,
unilocular, stigma simple, ovules 1-7. Fruit utricle, opening by bursting.
Seeds ovoid, with or without endosperm.