Herbs, perennial or rarely annual, rhizomatous or cespitose. Culms round or flattened in cross section. Cataphylls often present at culm base. Leaves: sheaths open; blade flat, channeled, ensiform or terete, sometimes septate, margins involute. Inflorescences terminal or pseudoaxillary, monochasia or dichasia, usually with monochasial branches, cymes or 1--many heads in racemes or panicles; bracteoles 2 or absent. Flowers: tepals (4--)6 in 2 whorls; stamens (2--)3--6. Capsules 1-locular or 3-locular, septicidal. Seeds many, ellipsoid to ovoid, sometimes tailed.