Cynanchum is a genus of about 300 species including some swallowworts, belonging to the family Apocynaceae. The taxon name comes from Greek kynos (meaning "dog") and anchein ("to choke"), hence the common name for several species is dog-strangling vine. Most species are non-succulent climbers or twiners. There is some evidence of toxicity.
These plants are perennial herbs or subshrubs, often growing from rhizomes. The leaves are usually oppositely arranged and sometimes are borne on petioles. The inflorescences and flowers come in a variety of shapes.
Like other species of the milkweed family, these plants bear follicles, which are podlike dry fruits.
These species are found throughout the tropics and subtropics. Several species also grow in temperate regions.
The root of Cynanchum atratum is used in Chinese traditional medicine and called Bai wei. Several other species had traditional Chinese medicinal uses.
Cynanchum as defined in the late 20th century (to include about 400 species) is polyphyletic and is being broken up. Species are being moved to genera including Orthosia, Pentarrhinum, and Vincetoxicum, with a group of mostly Old World species staying in Cynanchum, and old genera such as Raphistemma brought to synonymy. Revision of the genus taxonomy in 2023 identified two new synonyms: Vincetoxicum sibiricum f. linearifolium, described from Shandong, China in 1877, but long neglected and Cynanchum gobicum, previously believed to be endemic to Mongolia.
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