Aquatic, rootless, submerged, perennial, monoecious herbs; young plants green to olive green, older brown with thin, slender stems. Leaves whorled, 1-4 times dichotomously divided, much crowded towards the apex, stipulate; segments linear or filiform, often minutely toothed at irregular intervals with horny apices; horns usually 2, sometimes a glandular process is present in-between. Flowers minute, axillary, sessile, unisexual. Perianth or involucre 6-15, basally connate, subvalvate, apically terminated by 1-2 spines. Staminate flowers with 8-30 stamens on convex torus; filaments very short, broad, anthers 2-celled, extrorse, linear-oblong; connective projecting, apex truncate or provided with 2 sharp spines. Pistillate flowers greenish to orange-red with 1-carpelled, 1-locular, 1-ovuled, superior ovary; style subulate, stigma one-sided; ovule orthotropous pendulous. Fruit a 1-seeded nut, ellipsoidal or ovoid, with long persistent style and 2 sharp spines near the base, smooth, tubercled, winged or provided with 2-5 lateral spines. Seeds exalbuminous; embryo straight; cotyledons oval, thick.
An unigeneric family, with 10 (or 1 polymorphic) species, cosmopolitan in distribution.
Acknowledgements: We are grateful to the United States Department of Agriculture for financing this research under P.L. 480. Thanks are also due to Mr. B.L. Burtt, Dr. S. I. Ali and Dr. S. M. H. Jafri for helpful suggestions.
