Aquatic perennial, rarely terrestrial; roots all fibrous. Rhizome creeping. Stems slender to stout, prostrate or ascending, up to 1-(2) m long. Lvs divided into many filiform segments, glabrous but for a few short hairs at segment tips, (1)-3-6-(8) cm long; segments narrowly linear in terrestrial plants; petiole (2)-5-30 mm long. Fls solitary, 8-15 mm diam. Pedicels terete, glabrous, (2)-3-6-(8) cm long. Sepals 5, bluish near tip, reflexed, 2.5-4 mm long. Petals 5, white with yellow base, 6-8 × c. 4 mm long; nectary single, 0.5-1 mm from petal base, lunate. Receptacle usually with a few sparse hairs at base, elongating slightly at fruiting. Achenes 30-60, glabrous, ovoid, slightly flattened, transversely rugose; body 1.5-2 mm long; beak straight, c. 0.5 mm long.