Causonis is a genus of climbing vines in the family Vitaceae (the grape family), placed in the tribe Cayratieae. The genus was formally described by Constantine Samuel Rafinesque in 1830. It comprises around two dozen species native to tropical and subtropical Asia and the Southwestern Pacific, with some species also recorded from Africa and Australia.
Causonis was long subsumed within the broader genus Cayratia, but molecular phylogenetic studies revealed that old Cayratia was not monophyletic: Causonis japonica, the type species of Causonis, belongs to a lineage distinct from Cayratia pedata, the type of Cayratia. As a result, those species allied to C. japonica were reinstated under the older name Causonis. Within Vitaceae, the tribe Cayratieae — which includes Causonis — is most closely related to Tetrastigma and Cyphostemma.
Like other members of Vitaceae, Causonis species are twining or scrambling vines equipped with tendrils. They grow in forest edges, disturbed habitats, and secondary vegetation across tropical and subtropical Asia, reaching into the Pacific Islands and Australia. Some species, including the widely distributed Causonis trifolia and the type species Causonis japonica, have a long history of human use in traditional medicine and as food plants across their range.
Taxonomy Notes
Causonis was described by Rafinesque in 1830 but was long treated as part of the broadly circumscribed genus Cayratia. Molecular studies showed that old Cayratia was polyphyletic, with the C. japonica clade (Causonis) distinct from the C. pedata clade (true Cayratia). The genus was consequently resurrected, and species of the japonica alliance were transferred to Causonis. It sits in the tribe Cayratieae within Vitaceae, alongside relatives such as Tetrastigma and Cyphostemma.
Distribution
Causonis species are native to tropical and subtropical Asia and the Southwestern Pacific, with some species extending into Africa and Australia. The type species, Causonis japonica, ranges widely across East and Southeast Asia, while Causonis trifolia has a broad distribution across tropical Asia to the Pacific Islands.
