Description from Flora of China
Herbs, perennial. Taproot thickened, carrotlike. Stems erect. Leaves cauline, 3- or 4-verticillate, opposite, or alternate, sessile or shortly petiolate. Flowers large, terminal, solitary, pedicellate. Calyx lobes 5, shorter than hypanthium. Corolla bowl-shaped; lobes 5, shorter than or equaling tube. Stamens 5, free; filaments dilated into a triangular base, dilated part ciliate; anthers longer than filaments. Disk absent. Ovary semi-inferior, 5-locular, locules opposite calyx lobes; stigma 5-fid. Capsule 5-loculicidal at apex, valves with septa, opposite to calyx lobes. Seeds numerous, black or dark brown, large, terete, ellipsoid or oblong, longitudinally keeled.
One species: E Asia; widely cultivated elsewhere.
(Authors: Hong Deyuan (洪德元); Laura L. Klein, Thomas G. Lammers)