Description from Flora of China
Herbs sometimes biennial, subshrubs, or shrubs. Roots usually fibrous. Leaves opposite, petiolate or sessile, usually amplexicaul; leaf blade margin entire, dentate, crenate, or leaves pinnate. Inflorescences terminal, cymose, sometimes also with subterminal cymes and thus paniculate, many flowered; bracts small. Flowers bisexual, erect, 4-merous. Sepals free or basally subconnate, triangular to lanceolate, usually shorter than corolla tube. Corolla yellow (or white, red, pink, or orange), salverform; tube subquadrangular or basally inflated and urn-shaped, base slightly narrowed; lobes longer than tube. Stamens 2 × as many as petals, inserted near middle of corolla tube; filaments unequal in length, usually very short. Nectar scales linear to suborbicular. Carpels erect. Styles short or long. Follicles many seeded. Seeds ellipsoid.
About 125 species: Africa, Asia; four species (two endemic) in China.
(Authors: Fu Kunjun (Fu Kun-tsun); Michael G. Gilbert; Hideaki Ohba)