Herbs, perennial, cespitose, often with basal bulblike swellings, occasionally appearing rhizomatous, 0.3--3 dm, to 10 dm when floating or submersed. Culms erect or decumbent and rooting at nodes, or floating, terete, 1--2 mm diam., smooth. Cataphylls 1, straw-colored, apex acute. Leaves: basal 1, cauline 0--1; auricles 0.4--1 mm, apex acute, scarious; blade terete, occasionally filiform, flaccid, forming carpets, 2--10 cm x 0.8--1.4 mm. Inflorescences terminal racemes of 1--8(--30) heads, or single head, 2--10 cm, branches erect; primary bract erect; heads 2--6(--15)-flowered, obconic, 4.5--6.5 mm diam. Flowers often forming bulbils; tepals pale brown, ovate to lanceolate or inner oblong, 2--3.6 mm, nearly equal, apex acute to obtuse; stamens 3 or 6, anthers 3/4 to equal filament length. Capsules equaling perianth or exserted (to 0.5 mm beyond tepals), chestnut brown, 1-locular, cylindric, 2.5--4 mm, apex obtuse proximal to beak, valves separating at dehiscence. Seeds ellipsoid, 0.5--0.6 mm, not tailed; body clear yellow-brown. Fruiting mid summer--early fall. Margins and siliceous or peaty shores of pools and streams, often floating; 0--200 m; probably introduced in North America; St. Pierre and Miquelon; B.C., Nfld. and Labr. (Nfld.), N.S., Oreg.; Wash.; Europe; n Africa.