Description from Flora of China
Herbs or woody twiners, rarely erect, hairs usually stellate, rarely glabrous. Leaves petiolate, often cordate, margin entire, rarely dentate or lobed. Inflorescences axillary, often umbelliform or capitate cymes, less often scorpioid cymes, dense terminal spikes, or capitula, or solitary flowers; bracts linear, subulate (in China), or leaflike. Sepals equal or outer 3 often larger. Corolla blue, lilac, or pink, rarely white, funnelform or campanulate, with 5 distinct midpetaline bands; limb 5-toothed or subentire. Stamens included; filaments adnate to corolla basally; anthers ellipsoid; pollen globose, usually 5-zonocolpate, not spiny. Disc small or absent. Pistil included; ovary 2-loculed; ovules 2 per locule. Style 1, filiform; stigmas 2, elliptic or oblong, flat, rarely linear or globose. Capsule globose, 4- or 8-valved. Seeds 4 or fewer, smooth or minutely papillate, glabrous or velutinous, abaxial edges often with a narrow scarious wing.
Approximately 120 species: mainly in North and South America, a few species also in Africa and Asia; one species in China.