Bipolar disjunctions in Carex: Long-distance dispersal, vicariance, or parallel evolution?

The long-standing fascination of naturalists and scientists in the evolutionary and biogeographical causes behind the pattern of distribution of bipolar plants has lead to an intense debate around the three well-known biogeographical hypotheses of vicariance, long-distance dispersal, and parallel evolution. Genus Carex, despite lacking any general long-distance dispersal devices, represents six of the 30 plant species with bipolar distribution. We aimed to evaluate the role of the three alternative mechanisms mentioned above in the origin and evolution of five bipolar Carex species. Phylogenetic and phylogeographical reconstructions using Bayesian Inference, maximum parsimony, and statistical parsimony were performed with plastid (rps16 intron) and nuclear (ITS) DNA sequences. As a result, five cases of long-distance dispersal are proposed (C. canescens, C. macloviana, C. magellanica, C. maritima, C. microglochin s.str.) with an inferred southward migration from Northern to Southern Hemisphere for three of them. On the other hand, parallel evolution seems to be the most plausible explanation to understand the particular case of the bipolar species C. microglochin s.l.