Species limits and diversification in the Madagascar olive (Noronhia, Oleaceae).
Studies of ecological and phenotypic diversity in adaptive radiations have greatly contributed to our understanding of the patterns and processes of species diversification, whilst also challenging our assessment of the nature of species. Here, analyses of bioclimatic, molecular and morphological data, interpreted in phylogenetic and geographical contexts, were carried out to understand species limits in the Madagascar olive (Noronhia, Oleaceae). Most species hypotheses exhibit clear boundaries and are supported by at least one line of evidence, but a contrasting pattern of high morphological and ecological variation with relatively low nucleotide sequence divergence characterizes the diversification of Noronhia. This diversification was probably driven by fine-scale ecological and evolutionary processes, as suggested by the poor fit with four models of species diversification of the biota of Madagascar and the apparent lack of differentiation detected from large-scale bioclimatic data. Overall, this study offers useful insights into the patterns of plant diversification in Madagascar, the understanding of which requires good circumscription of species, improved knowledge of their distribution and operational models of diversification that take into account the particular biology of plants.