Description from Flora of China
Shrubs, less often trees, lianas, or suffrutescent herbs. Branches terete, 4-angled, or 4-winged. Leaves opposite, rarely alternate; stipules usually leafy, suborbicular and auriculate or reduced to a transverse line; petiole often short; leaf blade margin entire, crenate, or dentate. Inflorescences terminal and/or axillary, usually many-flowered; bracts mostly leaflike; bracteoles resembling sepals. Flowers 4-merous, bisexual or unisexual. Calyx campanulate or subcampanulate, less often cup-shaped or obconical, tube usually longer than lobes. Corolla campanulate, cup-shaped, salverform, or funnel-shaped; tube cylindrical, straight to curved, usually longer than lobes; lobes imbricate, rarely valvate. Stamens inserted on corolla tube, usually included, alternating with corolla lobes; filaments shorter to longer than anthers; anthers introrse, 2-locular, base usually deeply cordate. Ovary 2(--4)-locular, with several to many ovules per locule. Style short to long; stigma often large, clavate, capitate, or less often 2-lobed. Fruit a septicidally 2-valved capsule or in China only Buddleja madagascariensis a berry, many-seeded. Seeds small, often winged; endosperm fleshy; embryo straight.
About 100 species: tropics and subtropics of America, Africa, and Asia; 20 species and five hybrids in China.
Within China at least five recognizable hybrids are occasionally found of which three have been given hybrid epithets. These hybrids are intermediate between parental species and
are essentially impossible to key out.