Chloroplast sharing in the Tasmanian eucalypts

The biogeographic pattern of chloroplast DNA (cpDNA) haplotypes in Eucalypt us on the island of Tasmania is consistent with reticulate evolution, invol ving at least 12 Tasmanian species from the subgenus Symphyomyrtus. Intrasp ecific cpDNA polymorphism in 14 of 17 species is coupled with extensive sha ring of identical haplotypes across populations of different species in the same geographic area. Haplotype diversity is lowest in central regions of Tasmania formerly occupied by alpine vegetation during glacial intervals an d in northern regions that were periodically linked to continental Australi a by land bridges. The observed distribution of several cpDNA haplotypes un ique to Tasmania coincides with modeled locations of glacial refugia in coa stal areas of Tasmania and shows the power of cpDNA in unraveling the compl ex history of past distributions of Eucalyptus. The results suggest that th e model of evolution of the eucalypts should be reassessed to allow for the anastomosing effects of interspecific hybridization and introgression.