Spatial and lineage dependent processes underpin floristic assembly in the megadiverse Eastern South American mountains

Aim The astonishing diversity of ancient mountains was likely shaped by multiple evolutionary processes. However, there is an ongoing debate on what were the main processes driving the assembly of campos rupestres , the mega-diverse flora of Eastern South American mountains. Although the ancient nature of these mountains suggests their flora should be composed by relatively older lineages, they harbour a number of recently diverged clades. To better understand the evolution of ancient mountains’ floras, we tested if the campos rupestres are mainly composed by relatively old or recent communities and if angiosperm diversity is geographically structured using analyses of diversity and endemism. Location Eastern South America. Time period Oligocene/Miocene to the present. Major taxa studied Flowering plants. Methods We used analyses of diversity and endemism for 10% of the campos rupestres flora . We obtained distribution data from online databases, and phylogenetic hypotheses from the literature. With these datasets, we estimated alpha and beta metrics of taxonomic and phylogenetic diversity, and conducted categorical analyses of neo- and paleo-endemism. Results Phylogenetic overdispersion predominates in the campos rupestres . However, this general pattern is permeated by both lineage- and site-specific phylogenetic clustering, suggesting that recent diversification events depend on particular regional conditions and on the overall maintenance of old lineages. Although endemism patterns vary among different campos rupestres sites, paleo-endemism is widespread and particularly prominent where phylogenetic overdispersion is evident. Moreover, phylogenetic composition indicates variable past spatial connections across different sites, taxonomic composition is highly geographically structured and seems to be influenced by the vegetation surrounding the campos rupestres and/or by abiotic conditions. Main conclusions Our results reinforce the idiosyncratic nature of diversification patterns in ancient mountains and suggest that old, climatically buffered, infertile montane ecosystems not only include both relatively old and recent lineages, but that recent diversification is lineage and spatially dependent.