From Andes to the dry diagonal: phylogenomics and trait evolution elucidate the radiation of cacti in South American drylands.

The expansion of arid and dry ecosystems during the Miocene played a key role in the diversification of succulent plants; however, the relative contributions of biotic traits and environmental factors linked to aridity remain unclear. We investigate diversification in the cactus tribe Cereeae by integrating phylogenomic, biogeographic, and trait-based diversification analyses. We reconstructed a time-calibrated phylogeny and inferred ancestral ranges through biogeographic process-based modeling. We assessed diversification rate heterogeneity and evaluated the impacts of biotic traits and environmental variables using machine learning and trait-dependent diversification analyses. Our results indicate that Cereeae diverged in the late Miocene (∼9 Ma), with ancestral range spanning from the Central and Southern Andes to Espinhaço Mountain Range in Southeastern Brazil. Vicariance events, likely driven by marine transgressions and the assembly of the Cerrado savanna, promoted isolation of taxa across the Andes and Southeastern Brazil. Eastern Brazil was recolonized via jump dispersal during the Miocene-Pliocene transition. Diversification rates were strongly associated with rupicolous substrate preference and globose growth form, while environmental variables showed a negligible correlation with diversification. Our findings underscore the Southern Andes as a likely source of xerophytic lineages and highlight ecological specialization as the dominant driver of Cereeae radiation. This study demonstrates how integrative approaches can disentangle complex evolutionary processes, revealing that morphological innovation prevailed over environmental filtering in shaping the diversification of Cereeae in dry habitats.