Two independent dispersals to the Southern Hemisphere to become the most widespread bipolar Carex species: biogeography of C. canescens (Cyperaceae)

About 30 plant species occur at high latitudes in both hemispheres, thus achieving a so-called bipolar distribution. Six of these species belong to Carex, of which just one, Carex canescens, occurs on two different landmasses in the Southern Hemisphere (South America and Oceania). The goals of this study are (1) to test the various hypotheses accounting for the bipolar disjunction of C. canescens and (2) to elucidate if C. canescens migrated twice from the Northern Hemisphere to the Southern Hemisphere or if it dispersed from South America to Oceania (or vice versa). We obtained and analysed DNA sequences from the nuclear internal and external transcribed spacers (ITS and ETS) and from the plastid 5' trnK and rps16 introns from 57 populations of C. canescens spanning its bipolar range. We characterized the species distribution climatically by adding 1995 presence data points from the Global Biodiversity Information Facility. Our results suggest a Northern Hemisphere origin of C. canescens during the Pleistocene and two independent long distance-dispersal events to South America and Australia, by either direct dispersal or mountain-hopping. Long-distance dispersal appears to be the most widespread process resulting in the bipolar distribution of Carex spp.