Are there any widespread endemic flowering plant species in Macaronesia? Phylogeography of Ranunculus cortusifolius.

Abstract

Oceanic island endemics typically exhibit very restricted distributions. In Macaronesia, only one endemic angiosperm species, Ranunculus cortusifolius, has a distribution spanning the archipelagos of the Azores, Madeira, and Canaries. Earlier work suggested possible differences between archipelagos and the multiple origins of the species. This paper tests the hypothesis that R. cortusifolius is a single widespread Macaronesian endemic species with a single origin. Chloroplast (matK-trnK, psbJ-petA) and ITS sequences were generated from across the distribution of R. cortusifolius. Relationships were investigated using Bayesian inference and divergence times estimated using BEAST. Infraspecific variation was investigated using statistical parsimony. The general mixed Yule-coalescent model (GMYC) was further used to identify putative species boundaries based on maternally inherited plastid data. The hypothesis of multiple independent origins of R. cortusifolius is rejected. Divergence of the R. cortusifolius lineage from a western Mediterranean sister group in the late Miocene is inferred. Distinct genotypes were resolved within R. cortusifolius that are endemic to the Azores, Madeira, and the Canaries. Four to five putative species were delimited by different versions of the GMYC model. Ranunculus cortusifolius is the result of a single colonization of Macaronesia. The large distances between archipelagos have been effective barriers to dispersal, promoting allopatric diversification at the molecular level with diversification also evident within the Canaries. Isolation has not been accompanied by marked morphological diversification, which may be explained by the typical association of R. cortusifolius with stable and climatically buffered laurel forest communities.