Distribution: Occurring in lowland areas west of the Cascades crest in Washington; California; central U.S. and southern Canada east to northeastern U.S. and Canada; scattered locations elsewhere in U.S. and Canada.
Habitat: Pond and lake margins.
Origin: Introduced from eastern North America
Conservation Status: Not of concern
Herbaceous stoloniferous perennials with floating leaves, up to 115 cm, corms present.
Submersed or emersed, margins entire; leaves under water phyllodial, sessile, flattened above and beneath, up to 30-70 cm long, uncommonly widening into blade; leaves above water phyllodial, flattened above and beneath, or petioles triangular and 34-50 cm long, blade linear elliptic or uncommonly arrowhead- or narrowly arrowhead-shaped, 5-15 cm long and 0.6-12 cm broad, basal lobes shorter than remainder of blade when present.
Inflorescences bracteate racemes with 2-8 whorls, above water, 8-10 cm long and 2-6 cm broad; peduncles 10-115 cm long; bracts connate greater than or equal to ¼ total length, ovate, 3-6 mm, delicate, not papillose; fruiting pedicels not present; flowers imperfect, to 3 cm in diameter; sepals 3, curving backward, not encasing the flower, persistent; petals 3, white, deciduous; filaments widened, shorter than anthers, pubescent; anthers 2-chambered, splitting longitudinally; pistillate flowers sessile or nearly sessile, sterile stamens absent.
Fruiting heads 1-1.7 cm in diameter; achenes ovoid with abaxial keel, 2-3 mm long and 1.3-1.6 mm broad, beaked; face not tuberculate, wings 1 or 2, generally entire, glands 1; beak lateral and recurved, 0.8-1.4 mm.