Description from Flora of China
Herbs annual, biennial, or perennial, usually glabrous. Stems erect to decumbent. Leaves opposite or alternate, rarely verticillate, short petiolate to sessile, margin entire. Flowers solitary, axillary, 5-merous. Calyx parted nearly to base; lobes spreading. Corolla blue, red, or white, rotate or infundibuliform; tube very short or obsolete; lobes contorted in bud. Stamens attached at base of corolla; filaments usually pubescent; anthers ellipsoid, apex obtuse, dorsifixed. Ovary ovoid; style filiform; stigma obtuse. Capsule globose, circumscissile, many seeded.
Approximately 28 species distributed throughout the temperate zone in Africa, Asia, Europe, North America, and South America; one species occurs in China.