Perennial scapigerous herbs of wet habitats, rhizomatous; rhizome short, with fibrous roots. Leaves basal or cauline, sheathing at the base, linear, ensiform or flat and dilated, entire, often tapering above. Inflorescence fascicled umbellate cymes, terminal; involucre with 2 or 3 bracts. Flowers 3-merous, hermaphro¬dite, actinomorphic, usually long pedicelled. Perianth 2-seriate, persistent, the outer 3 sepal-like, imbricate, shorter than the inner whorl of 3 petal-like, imbricate segments, usually thin and deciduous, rarely absent. Stamens usually 6-9, rarely 5 or numerous, very variable, outer usually sterile; filaments flattened or linear, short or long, free, hypogynous; anthers basifixed, 2-celled, ovate to oblong, longitudinally dehiscent, introrse. Carpels (3-) 9 (or many), superior, whorled, free or basally connate, sessile on a flat receptacle; styles very short, terminal on each carpel; ovules numerous, anatropous, scattered on branched reticulate, parietal placentas. Fruit of 6-many seeded follicles, each follicle free or nearly so, opening by the ventral side. Seeds minute, smooth, exalbuminous; embryo straight.
An unigeneric family, chiefly of the temperate Eurasia, sometimes included under Alismataceae (Bth. & Hook. f., Gen. Pl. 3: 1008. 1878; Hook. f., Fl. Brit. Ind. 6: 559. 1893) from which it differs by the absence of latex, leaf shape, inflorescence, introrse anthers, numerous scattered ovules and straight embryo.
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.