Glabrous, annual or perennial herbs. Leaves distichous, radical, entire, linear, with a sheath. Inflorescence terminal, spicate or racemose. Flowers bisexual, actinomorphic, small, inconspicuous, mostly green. Perianth segments 6, conchiform. Stamens 6 (or partly reduced), epi-tepalous. Anthers sessile, extrorse, cells 2. Carpels 6, or less by abortion, free or united, or partly free; ovule 1 per cell, basal, erect; style mostly absent. Pericarp dry. Seed exalbuminous, embryo straight. Distr. Cosmopolitan, the majority of the ca 15 spp. known from the S. hemisphere. The Malaysian species is the only one of subg. Cycnogeton (ENDL.) BUCH., distinct by entirely free carpels.