Trees deciduous. Leaves simple, purple glandular punctate at vein axils abaxially. Inflorescences paniculate, corymbose, or racemose, terminal. Calyx bilabiate or irregularly divided, globose in buds. Corolla campanulate, bilabiate, upper lip 2-lobed, lower lip 3-lobed. Fertile stamens 2, included, inserted at base of corolla tube; staminodes 3. Disc conspicuous. Ovary 2-locular; ovules several. Capsule dehiscing loculicidally, long terete; valves thin; septum slender, terete. Seeds in several rows, rounded, thin membranous, with hair tufts at both ends.

About 13 species: N America and E Asia; four species in China.