Stem erect, 30-70 cm. Leaves opposite or 3-verticillate; leaf blade narrowly elliptic-oblong, oblong-ovate, ovate, or broadly so, 2.5-10 × 0.8-5 cm, base attenuate, margin entire, ± undulately dentate, or dentate, apex obtuse to acute. Cyme flat topped, dense, 7-11 cm wide. Flowers ca. 1 cm in diam. Sepals linear-lanceolate to broadly lanceolate, ca. 1 mm, apex acuminate. Petals purplish red to purple, lanceolate to broadly so, 4-5 mm. Stamens longer than corolla, 6-8 mm; anthers violet. Nectar scales rectangular, 1-1.2 mm, apex emarginate. Carpels narrowly ellipsoid, ca. 3 mm. Styles ca. 1.2 mm. Follicles erect. Fl. Aug-Sep, fr. Sep-Oct.