Scapigerous aquatic or marsh herbs, with mostly linear radical leaves, sheathing below and without a distinct ligule. Inflorescence raceme or spike. Flowers small, hermaphrodite or unisexual, actinomorphic or slightly oblique, 2-3-merous, bractless, protogynous. Perianth segments 6, in 2 series, herbaceous, greenish, whitish or purplish. Stamens (4- ) 6 with very short filaments (almost sessile), hypogynous. Carpels (4- ) 6, sometimes 3 sterile, free or connate, superior, each I-celled with 1, basal anatropous ovule; style absent or short; stigma papillose or pencillate. Fruit indehiscent or tardily dehiscent, semicomposite, apparently like a capsule but carpels often separating on maturity with 1 seed in each; seed erect, exalbuminous with straight embryo.