Distribution: Both sides of the Cascades in Washington; throughout most of North America.
Habitat: Nonalkaline wetland, riparian, pond and lakeshore sites at low to moderate elevations.
Growth Duration: Perennial
Conservation Status: Not of concern
Perennial herbs from elongate rhizomes, the simple or branched square stems 2-8 dm. tall, glabrous except for the hairy nodes.
Leaves opposite, all cauline, numerous, lanceolate, 3-8 cm. long and 1-3.5 cm. wide, tapering to a short petiole, irregularly deeply toothed, the lower teeth the larger.
Flowers sessile, verticillate in the axils of scarcely reduced leaves; calyx with 5 firm, narrow, sharp-pointed lobes; corolla white, small, about equally 4-lobed, 2-3 mm. long, about equaling the calyx; fertile stamens 2, barely exerted, sterile stamens 2, small, club-shaped; style 2-parted; ovary 2-celled, superior.
Nutlets 4, with corky ridges around the tip.