Description from Flora of China
Shrubs scandent, glabrous except for flowers. Leaves with numerous lateral veins and a well-defined intramarginal vein. Cymes terminal and extra-axillary, lax. Calyx glands 5. Corolla rotate; tube short; lobes obtuse, usually hairy inside, overlapping to right. Corona inserted at base of corolla; lobes 3-fid, central segment threadlike, inflexed; lateral segments short, broad, flaplike. Filaments short, distinct; anthers dorsally hairy, connivent, adnate to stigma head; apical appendages incurved; pollen tetrads in masses, attached to a common retinaculum. Style short; stigma head convex. Follicles paired, somewhat divergent, sometimes adhering at tips.
About 10 species: temperate Asia, southern Europe, tropical Africa; five species in China (but see also Browicz's monograph of the genus [Arboretum Kùrnickie 11: 1-104. 1966], which recognized in China only two species, one with three subspecies).