Beyond climate: convergence in fast evolving sclerophylls in Cape and Australian Rhamnaceae predates the mediterranean climate

1. Morphological convergence in mediterranean-type ecosystems (MTEs) has long been interpreted as adaptation to climatic similarities among the five MTEs of the world. Here, we challenge this model using the globally distributed Rhamnaceae. 2. We collected functional trait data (specific leaf area, leaf area, spinescence, leaf phenology, growth form and leaf margin type) and biome data to test for trait convergence in MTEs, for models of trait evolution and ancestral state reconstruction and for the effect of traits on speciation and extinction rates, using a phylogenetic framework. 3. We show that leaf functional traits evolve to three optima, which correspond to (i) the edaphically specialized Australian and Cape MTEs (AC), (ii) the mediterranean-type climates, but edaphically normal Chile, California and Mediterranean Basin (CCM) and (iii) the non-mediterranean habitats. We find that Rhamnaceae in CCM are predominantly characterized by non-sclerophylly, the ancestral state in Rhamnaceae, and Rhamnaceae in AC by sclerophylly. These leaf character syndromes have evolved prior to mediterranean climates in MTEs, thereby failing to be adaptive to this selective regime. However, sclerophylly evolved contemporaneously with the transitions to AC and may therefore be an adaptation to nutrient-poor soils. 4. The evolution of sclerophylly has contributed to increased diversification rates of Pomaderreae in Australia and Phyliceae in the Cape, by reducing extinction rates and thereby facilitating evolutionary persistence. The historical relatively stable conditions in AC are consistent with this persistence hypothesis. 5. Synthesis. In this study, we integrate the fields of macroevolution and ecology and show that low extinction rates may not only account for the ecological, but also for the floristic dominance of sclerophylly in the hyperdiverse Australian and Cape mediterranean-type ecosystems.