Herbs, to 1 m. Leaves emersed, petiolate; blade linear-lanceolate to broadly elliptic to ovate, to 30 ´ 1--12 cm. Inflorescences to 1 m. Flowers chasmogamous; sepals 1.7--3.2 mm; petals purplish white to purplish pink, 3.4--6.4 mm, margins ± erose, apex obtuse; anthers ellipsoid, 0.7--1.4 mm; style ± straight, 0.6--1.5 mm, exceeding ovary length. Fruiting heads 4--6.5 mm diam; achenes ovoid, 1.7--3.1 mm, abaxial keels broadly rounded, with 1 median abaxial groove, rarely 2, beak erect or nearly erect. 2n = 14 (Eurasian material).

Flowering and fruiting late summer. Stream margins; 200 m; introduced; Alaska; Eurasia.

The name Alisma plantago-aquatica has been used in a variety of North American floras. We are following, however, the treatment of I. Björkqvist (1968), in which the native distribution of A. plantago-aquatica is restricted to Eurasia.