Evolutionary history, taxonomy, and ecology of Neotropical Cissus (Vitaceae) in the biotic transition zone of Mexico and Central America

BACKGROUND AND AIMS: Mexico constitutes a biotic transition zone between Nearctic and Neotropical floras, which alongside its complex geography and climatic variability makes it an especially diverse region. Cissus, the largest genus of Vitaceae, has c. 70 species in the Neotropics, with 20-25 species in Mexico and Central America, occupying diverse environments from tropical forests to deserts. Despite its ecological relevance in the area, Neotropical Cissus species have been barely studied. Here we aim to address the phylogenetic history, taxonomic delimitation, biogeography, and ecological preferences of Cissus in the biotic transition zone of Mexico and Central America. METHODS: We obtained nuclear and plastid phylogenies of Neotropical Cissus using target enrichment Hyb-Seq, sampling c. 50% of the Neotropical species and most Mexican species. We performed time calibration and biogeographic analyses to assess the colonization history, performed ancestral reconstructions of relevant taxonomic traits, and studied geographic and climatic differences between clades and species in Mexico and Central America using climatic principal component analyses. KEY RESULTS: Four main clades were retrieved in Neotropical Cissus via phylogenomics, with putative early hybridization detected between clades. Morphological examination and phylogenetic data provided support for taxonomic reassessment in Mexico. Biogeographic analyses pointed to several colonization events to Mexico during the Oligocene and the Miocene, with xeric species from western Mexico clustering in a single mid Miocene lineage. Climatic and geographic analyses supported differences between clades, and mountain ranges were suggested to have acted as geographic and climatic barriers for some lineages. CONCLUSIONS: Our research recovered four main clades with significantly distinct geographic and climatic preferences in Neotropical Cissus. Mexico was colonized several times and geographic and climatic isolations were crucial for speciation. Our results highlighted the presence of hidden species diversity in Mexico, underscoring the need for integrative biodiversity discovery in the Mexico transition zone.