Distribution: Widespread in the United States and Canada; occasional at lower elevations in the Pacific Northwest.
Habitat: Slow-moving streams and ditches.
Flowers: June - July
Origin: Introduced from Europe
Conservation Status: Not of concern
Glabrous, short-lived perennial from fibrous roots, the stems usually erect, 2-10 dm. tall.
Leaves opposite, sessile and clasping, elliptic-ovate to elliptic-oblong, 3-5 times as long as wide, entire.
Inflorescence of few-flowered racemes on long peduncles arising in the leaf axils; calyx of 4 broad, blunt sepals; corolla white to pink, rotate, 4-lobed, the upper lobe the largest, about 5 mm. wide; style 1.5-2.5 mm. long; pedicels spreading, 3-8 mm. long; stamens 2.
swollen, 2.5-4 mm. high and a little wider, shallowly notched.