Description from Flora of China
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.