Description from Flora of China
Herbs prostrate or erect to twining to several meters tall, rhizomatous [or woody at base]. Leaves subsessile to petiolate, oblong to hastate or sagittate [or rarely pedate]. Inflorescences axillary, 1-flowered [or few-flowered] cymes; bracteoles 2, sepal-like, inserted immediately below calyx, ovate and sometimes saccate, enclosing calyx [or remote from calyx and subulate or leaf-shaped], persistent. Sepals subequal, persistent. Corolla white, pink [or pale yellow], funnelform, with 5 distinct midpetaline bands, glabrous. Stamens included, equal. Pollen globose, pantoporate, not spiny. Ovary 1-loculed, 4-ovuled. Style 1, included in corolla; stigmas 2, clavate. Capsule globose, glabrous, indehiscent. Seeds 4, smooth or minutely tuberculate.
Approximately 70 intergrading subspecific taxa which can be arbitrarily combined into about 25 species: mostly temperate but sparingly extending to the tropics; six species in China.
Nearly all taxa in Calystegia intergrade geographically into neighboring taxa with the exception of the widespread coastal species, C. soldanella (Linnaeus) R. Brown. Almost half of
the genus is endemic in California, U.S.A., and the exceptions noted in the generic description in brackets [ ] all refer to the Californian endemics. It is impossible to draw clearly defined
specific limits, and intermediate forms are always found where two taxa approximate geographically.
(Authors: Fang Rhui-cheng; Richard K. Brummitt)