Herbs, perennial, rhizomatous, caulescent; turions absent. Leaves alternate, floating [submersed], petiolate [sessile]; sheath not persisting longer than blade, not leaving circular scar when shed, not ligulate, not auriculate; blade ovate to narrowly lanceolate [linear]; intravaginal squamules (i.e., minute appressed, planate trichomes attached at basal edge) scales, more than 2. Inflorescences terminal, spikes, subtended by spathe, pedunculate; peduncle following fertilization not elongating, not spiraling. Flowers bisexual [unisexual]; subtending bracts absent; perianth present [absent]; tepals 1[--6]; stamens 6--18[--50] in 2--3[--4] series, not epitepalous; anthers distinct, dehiscing longitudinally; pollen ellipsoid; pistils 2--6[--9], distinct, not stipitate; ovules basal-marginal, anatropous. Fruits follicles. Seeds 4; embryo straight.