Fls mostly bisexual, small, actinomorphic or slightly oblique, in spike or raceme, without bracts. Tepals 6 in 2 whorls, greenish or reddish. Stamens 6 or 4; filaments very short; anthers 2-celled, extrorse, opening by longitudinal slits. Carpels 6 (sts 3 sterile) or 4, superior, free or ± connate; style short or absent, stigma plumose or papillose; ovule 1, basal, us. erect, anatropous. Fr. dry. Seed without endosperm. Annual or perennial, rhizomatous, scapigerous, glab. herbs of wet places. Lvs mostly radical, linear, sheathing at base. Fls protogynous, wind-pollinated. Genera 4; widely distributed, the other 3 confined to S. Hemisphere.