Lineage diversification and hybridization in the Cayratia japonica-Cayratia tenuifolia species complex

- Phylogenetic relationships in the Cayratia japonica-Cayratia tenuifolia species complex were resolved.
- Accessions from Australia and Asia formed distinct monophyletic clades.
- Details of cryptic divergences and hybridizations in the Asian group were revealed.
- Major divergences within the Asian clade likely occurred in the Tertiary era.

The Cayratia japonica-Cayratia tenuifolia species complex (Vitaceae) is distributed from temperate to tropical East Asia, Southeast Asia, India, and Australia. The spatiotemporal diversification history of this complex was assessed through phylogenetic and biogeographic analyses. Maximum parsimony, neighbor-joining, and maximum likelihood methods were used to analyze sequences of one nuclear (AS1) and two plastid regions (trnL-F and trnC-petN). Bayesian dating analysis was conducted to estimate the divergence times of clades. The likelihood method LAGRANGE was used to infer ancestral areas. The Asian C. japonica and C. tenuifolia should be treated as an unresolved complex, and Australian C. japonica is distinct from the Asian C. japonica-C. tenuifolia species complex and should be treated as separate taxa. The Asian C. japonica-C. tenuifolia species complex was estimated to have diverged from its closest relatives during the Late Eocene (35.1 million years ago [Ma], 95% highest posterior densities [HPD] = 23.3-47.3 Ma) and most likely first diverged in mid-continental Asia. This complex was first divided into a northern clade and a southern clade during the middle Oligocene (27.3 Ma; 95% HPD = 17.4-38.1 Ma), which is consistent with a large southeastward extrusion of the Indochina region relative to South China along the Red River. Each of the northern and southern clades then further diverged into multiple subclades through a series of dispersal and divergence events following significant geological and climatic changes in East and Southeast Asia during the Miocene. Multiple inter-lineage hybridizations among four lineages were inferred to have occurred following this diversification process, which caused some Asian lineages to be morphologically cryptic.