Description from Flora of China
Herbs erect, perennial and often woody at base, juice watery. Leaves opposite; petiole short, intra- and interpetiolar glands present; leaf blade herbaceous to somewhat leathery, entire. Flowers terminal and axillary, solitary or rarely in 2- or 3-flowered cymes. Sepals small, narrowly oblong, awl-shaped, without glands. Corolla purple, red, pink, or white, salverform; tube glabrous or sparsely puberulent, throat constricted, woolly to velvety; lobes spreading, obliquely obovate, overlapping to left, apex apiculate. Stamens inserted in widened portion of corolla tube; anthers free, oblong, base obtuse; disc of 2 glands. Ovaries 2; ovules numerous. Style filiform; pistil head with a cylindric base and reflexed hyaline frill. Follicles 2, cylindric, apex acute. Seeds black, oblong, testa rugose.
Eight species: seven endemic to Madagascar, one restricted to India and Sri Lanka; one species cultivated in China.