Tufted or shortly rhizomatous, grass-like, annual or perennial. Stems usually compressed, ± winged. Leaves linear, distichous, equitant, basal and cauline. Inflorescence of several subumbellate clusters of 2-many pedicellate flowers emerging successively from a usually 2-valved spathe. Flowers small, cream, blue or violet, rarely white, delicate and fugacious, closing at night, usually cup-shaped below, spreading above; lobes free almost to base, ± equal, often apiculate, outer wider than inner. Stamens inserted at base of perianth, filaments usually united in a cylindrical tube. Style-branches entire. Capsules globose, exserted from spathe-values on elongate filiform pedicels. Seeds numerous, globose, black, ± pitted. Spp. c. 100, mostly of N. and S. America, 1 from Hawaii, 1 from Ireland. Adventive spp. 4.