Chloroplast DNA Polymorphism Signals Complex Interspecific Interactions in Eucalyptus (Myrtaceae)

Variation in the chloroplast genome of 44 accessions representing 14 Eucalyptus L'Her. species from the series Viminales (sensu Pryor and Johnson 1971) was investigated. Southern analysis of the chloroplast genomes restricted with 12 enzymes revealed 20 restriction-site polymorphisms of which 7 were autapomorphic to individual trees. The 13 informative restriction-site polymorphisms were distributed between individuals of different species, but none was species-specific. Fourteen chloroplast haplotypes were identified for south-eastern Australian individuals. In endemic Tasmanian species, five haplotypes were identified. Chloroplast haplotypes appear to have a mosaic distribution in south-eastern Australia, more closely associated with geographical regions than with morphological species boundaries. The biogeographic distribution of chloroplast haplotypes may be explained by a combination of interspecific hybridisation and introgression, and convergent evolution. The lack of species-specificity of cpDNA variation indicates that, although cpDNA is not appropriate for species-level phylogeny analysis in the series Viminales, it may provide useful information in studies of biogeography and gene flow in Eucalyptus.