marine perennial herbs, with creeping rhizomes. Leaves linear, alternate or
apparently opposite, distichous, sheating at base, ligule at the juncture of
sheath and blade. Flowers small, monoecious or dioecious, unisexual,
hydrophilous, naked or rarely minutely bracteates, borne in axillary cymes or
racemes of cymes, or solitary. Male flower of 2 long pedicelled, 2-celled
anthers, anthers paired on a common filament, or sessile. Female flower of 1 or
(2) carpels, sessile or stipitate, styles and stigma filifform, ovule solitary.
Fruit a 1-seeded nutlet. Fruit small,
hard and indehiscent.