Perennial, usually rhizomatous, less often annual herbs, glabrous or with hairy leaf margins; rarely leaf abaxial surface with simple, many-celled trichomes. Silica bodies ±absent; oxalate raphides absent; stomata paracytic. Stem erect to ascending, rarely procumbent, usually terete, leafless or leaf-bearing. Leaves linear or filiform, spirally arranged, rarely distichous; sheath closed or open, often auriculate; auricles rarely joined to form a ligule-like structure; blades of basal leaves sometimes reduced (cataphylls). Inflorescence terminal, rarely pseudolateral (bract resembles a continuation of stem), compound, cymose or racemose, panicle-like or anthelate, many-flowered with flowers in many to one terminal heads or spike-like clusters; lower inflorescence bracts usually herbaceous; each branch with membranous bract and adaxial prophyll; flower bracteoles 1–2 or absent; rarely inflorescence reduced to a single terminal or lateral (subterminal) flower. Flowers small, usually up to 8 mm long (rarely to 40 mm), actinomorphic, hypogynous, usually hermaphrodite, rarely unisexual (dioecious or monoecious). Perianth segments 6, in two whorls, glumaceous, usually ±equal, free. Stamens 6 in two whorls or inner whorl reduced; filaments filiform to flattened; anthers 2-thecate, 4-sporangiate, oblong to linear, basifixed, dehiscence lateral; connective rarely with a projection; pollen in tetrads. Carpels 3, connate; ovary superior, unilocular or 3-septate to 3-locular; style 1, distally 3-branched (stigmas), papillae ±adaxial. Fruit an orbicular to oblong-ellipsoid loculicidal (rarely circumscissile) capsule. Seeds 3–many; endosperm starchy; embryo small, broadly cylindric; outer seed-coat hyaline, whitish to brownish, loose to adpressed, sometimes forming apical and/or basal appendages; inner seed-coat usually brown to castaneous.