Description from Flora of China
Herbs annual or perennial, glabrous or pubescent with simple hairs. Leaves mostly equal, sometimes paired, simple, petiolate; leaf blade membranous, entire, denticulate or sinuate. Inflorescences solitary flowers in leaf axils or branch forks. Flowers actinomorphic, 5-merous. Calyx campanulate. Corolla yellow or white, often with a contrasting eye, rotate or rotate-campanulate, subentire or lobed. Stamens shorter than corolla, inserted at base of corolla tube; filaments sometimes expanded at base; anthers dehiscing longitudinally. Ovary 2-locular, ovules numerous. Stigma minutely 2-lobed. Fruiting calyx becoming enlarged, inflated, entirely enveloping fruit, membranous or leathery, with 5 or l0 longitudinal ribs, base often invaginated. Fruit a juicy globose berry. Seeds numerous, compressed, discoid or reniform, minutely pitted; embryo coiled, subperipheral.
About 75 species: mostly in the Americas, a few in Asia and Europe; six species in China.
The genus embraces many species from the New World that have green fruiting calyces, and several have been introduced to China. Many Chinese collections with green fruiting
calyces could not be determined, and their identity is to be sought among the more than 70 species distributed in various parts of the New World, a task for future workers.