Description from Flora of China
Herbs perennial or subshrubs, ascending or procumbent, sometimes climbing, with lower branches ± woody, sometimes glandular. Leaves opposite, subequal, often fleshy, margin entire or undulate. Inflorescences terminal or axillary, pedunculate, umbels or verticils, sometimes grouped into panicles. Flowers bisexual. Perianth constricted beyond the ovary, limb funnelform, white, pink, or purple, 5-lobed. Stamens (2-)3(-6), often long exserted; filaments linear, unequal, connate at base. Ovary stipitate. Style linear, exserted; stigma peltate. Fruit clavate or obconic, 10-ribbed, with large, raised, wartlike sticky glands. Seed erect; embryo curved; cotyledons enclosing the scanty endosperm.
About 25 species: tropical and subtropical regions, mostly in Africa and S Arabia; two species (one endemic) in China.