Dorstenia, the second largest genus (105 species) within the Moraceae, is the only genus in the family with woody, herbaceous and succulent species. All but one species of Dorstenia are restricted to the Neotropics or Africa, and it is the only genus in the family with an almost equal transatlantic distribution. This work presents the first molecular phylogeny and the first evolutionary study to examine origin and diversification within the genus. We inferred the phylogeny with ITS sequence data using Bayesian and maximum likelihood approaches. We tracked the evolution of distinct morphological characters and tested for correlated evolution in multiple characters. Time and place of Dorstenia’s origin were estimated to test a post-Gondwanan versus a Gondwanan origin hypothesis using fossil calibrations, Bayesian molecular dating, and maximum likelihood-based ancestral range reconstructions. Our phylogenetic analysis supports the monophyly of Dorstenia; previous subgeneric classifications are polyphyletic and must be re-evaluated. Woody habit, phanerophytic life form, macrospermy, and lack of storage organs are ancestral traits found in African Dorstenia. Evolution of woodiness and macrospermy are correlated. Dorstenia appears to have originated in Africa, radiated into the Neotropics and subsequently re-colonised Africa. Whether or not the extant distribution is the result of vicariance or dispersal is equivocal.

Correlations between the amount of energy received by an assemblage and the number of species that it contains are very general, and at the macro-scale such species–energy relationships typically follow a monotonically increasing curve. Whilst the ecological literature contains frequent reports of such relationships, debate on their causal mechanisms is limited and typically focuses on the role of energy availability in controlling the number of individuals in an assemblage. Assemblages from high-energy areas may contain more individuals enabling species to maintain larger, more viable populations, whose lower extinction risk elevates species richness. Other mechanisms have, however, also been suggested. Here we identify and clarify nine principal mechanisms that may generate positive species–energy relationships at the macro-scale. We critically assess their assumptions and applicability over a range of spatial scales, derive predictions for each and assess the evidence that supports or refutes them. Our synthesis demonstrates that all mechanisms share at least one of their predictions with an alternative mechanism. Some previous studies of species–energy relationships appear not to have recognised the extent of shared predictions, and this may detract from their contribution to the debate on causal mechanisms. The combination of predictions and assumptions made by each mechanism is, however, unique, suggesting that, in principle, conclusive tests are possible. Sufficient testing of all mechanisms has yet to be conducted, and no single mechanism currently has unequivocal support. Each may contribute to species–energy relationships in some circumstances, but some mechanisms are unlikely to act simultaneously. Moreover, a limited number appear particularly likely to contribute frequently to species–energy relationships at the macro-scale. The increased population size, niche position and diversification rate mechanisms are particularly noteworthy in this context.