Phylogeny, character evolution and taxonomic revision of Causonis, a segregate genus from Cayratia (Vitaceae)

Causonis (Vitaceae) is widely distributed in the tropical, sub-tropical and temperate regions from Asia to Australia. The genus was established by Rafinesque in 1830 but included under Cayratia by Gagnepain in 1911. Generic status of Causonis was restored in 2013, but circumscription of the genus and its species remained poorly understood. Here, we sample 92 accessions of Causonis to reconstruct the phylogenetic relationships within the genus using four chloroplast loci (atpB-rbcL, trnC-petN, trnH-psbA, trnL-F) and three nuclear loci (AS1, At103, ITS). Both the chloroplast and nuclear data support the monophyly of Causonis, and relationships among major clades of the genus are well-supported based on the chloroplast data. The first diverged clade consists of two species both endemic to Australasia. Evolutionary trends of eight morphological characters are tested through ancestral character state reconstruction using the chloroplast dataset. We recognize 16 species and 4 varieties in Causonis, including two new species: C. australasica sp. nov. and C. glauca sp. nov. We herein make 10 new combinations for eight species and two varieties. The widespread Causonis japonica is also redefined based on morphological and molecular evidence.

Automated summary

Causonis, a widely distributed genus in tropical, sub-tropical, and temperate regions from Asia to Australia, was confirmed to be monophyletic based on both chloroplast and nuclear gene data. The study identified 16 species and 4 varieties within the genus, including two new species. The evolutionary trends and relationships among major clades of Causonis were well-supported by the chloroplast data.