Description from Flora of China
Herbs, delicate annual or perennial. Leaves opposite along stem and/or in a whorl at base, subsessile; stipules absent. Flowers axillary and/or terminal, solitary or in pedunculate umbel-like cymes which sometimes rebranch to form irregular compound umbels, 4-merous, white or yellow, rarely pale blue. Calyx campanulate, 2--4-lobed; lobes valvate. Corolla campanulate [salverform or urceolate], often bearded at mouth, tube short to long, lobes exduplicate-valvate in bud. Stamens inserted on lower half of corolla tube; filaments much longer than anthers; anthers introrse, extrorse, or rarely latrorse, included to slightly exerted, 2-locular. Pistil glabrous. Ovary superior to slightly inferior, with many ovules per locule. Style one, base usually parted, rarely 2 separate styles; stigma capitate or 2-cleft. Capsules globose to subglobose, opening by apical loculicidal slits, 2-horned, horns terminated by a style which may be split or remain partly connate, many-seeded. Seeds minute, cylindric-ellipsoid to angular; seed coat thin reticulate to verrucose or almost very minutely papillate; endosperm fleshy.
About 40 species: mainly Australia, extending to E, S, and SE Asia and Pacific Islands; two species in China.