Stems erect, 1 or several and cespitose, 40-100 cm tall or more, usually simple, with sterile branches in leaf axils, with a ring at each node connecting petiole bases, glabrous or apically very sparsely white villous. Leaves opposite, occasionally in whorls of 3 or 4; petiole 2-4(-10) mm; leaf blade lanceolate, 4-15 X 1-3 cm, glabrous or with short curly hairs, base rounded to broadly cuneate to sometimes cordate, margin deeply serrate, and often partly double serrate, apex acuminate. Inflorescences 1 or several, never in a large panicle, with white short curly hairs. Pedicel straight, ca. 2 mm. Corolla purple to blue, 5-6 mm; tube 2/5-1/2 of corolla length; lobes patent, upper lobe ovate, other 3 lobes narrowly ovate. Stamens conspicuously exserted. Capsule ca. 3 mm, glabrous. Persistent style ca. 7 mm. Fl. Jun-Aug. 2n = 34, 64, 68, 70.