Mostly small perennial herbs of cespitose habit and of aquatic or marsh habitats, acaulescent or nearly so, roots fibrous; leaves mostly linear, basal grass like, usually crowded, often pellucid, sometimes membranous; plants usually monoecious or rarely dioecious; inflorescence a small head subtended by an involucre of bracts and borne capitately on an erect, slender, often scapose peduncle that usually much exceeds the leaves and is sheathed basally; flowers unisexual, regular or rarely irregular, small to minute numerous, sessile to shortly pedicellate, on a variously shaped torus or receptacle, each flower usually borne in a axile of a scarious, scale like, colorless or colored bract; when plants are monoecious the staminate and pistillate flower either mixed within the inflorescence or the staminate in center and pistillate on the periphery; when dioecious the flowers of an entire head of one sex or the other; perianth chaffy or membranous, rarely hyaline, in 2 series , outer series  free or the segments coherent, the iner steries stipitate, stamens as many or twice as many as outer perianth segments and alternate with them, inserted on corolla, the anthers 1-2 celled, introrse, dehiscing by vertical slits, pistillate flower unipistillate the ovary 2-3 loculed, superior, each locule with a single pendulous orthotropous ovule, the placentation axile, style 1 terminal as many branches as ovary locules, each branch simple or forked, staminodes rarely present; fruit a membranous 2-3 celled, 2-3 seeded loculicidal capsule, embryo  minute and apical.