Distribution: Occurring east of the Cascades crest in Washington chiefly along the Columbia River; British Columbia to California, east to the Great Lakes region and midwestern U.S.
Habitat: Wet places, often where alkaline.
Conservation Status: Threatened in Washington (WANHP)
Simple to branched annual, the stem 5-40 cm. tall.
Leaves opposite, entire, oblong to oblong-lanceolate, 2-4 cm. long and 2-8 mm. broad, cordate-clasping at base.
Flowers 1-5 in cymes in the leaf axils, sessile; calyx strongly 8-ribbed and 4-angled, bell-shaped, 2-3 mm. long, with small teeth in the sinuses; petals short-lived, purplish, 1 mm. long; stamens 4; style slightly exerted, 1-1.5 mm. long; stigma discoid.
Capsule 4-celled, membranous, globose, 4 mm. long.