Stems prostrate, 0.2-1 mm thick. Leaf blades linear or filiform, 0.7-3 × 0.04-0.1 cm. Flowers: sepals 1-2 mm; petals 3-5 × 1-2.5 mm. 2 n = 32.

Flowering late spring-summer (Jun-Sep). Shallow water and wet ground, open shores of lakes and rivers and in temporary ponds; 0-2500 m; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., Que., Sask., Yukon; Alaska, Conn., Idaho, Maine, Mass., Mich., Minn., Mont., N.H., N.J., N.Y., Pa., Vt., Wash., Wis., Wyo.; Eurasia.