Conservation genetics and phylogenetics of New Caledonian Retrophyllum (Podocarpaceae) species

Retrophyllum is a genus in the Podocarpaceae consisting of five species with a disjunct distribution in the Southern Hemisphere. Support for the monophyly of the genus, and its sister group relationship to an Afrocarpus-Nageia clade, was obtained from trnL-F sequences. Within Retrophyllum, the Melanesian species (R. minus, R. comptonii, R. vitiense) formed a monophyletic group, sister to the South American species R. rospigliosii. This topology is consistent with Gondwanan fragmentation, although the amount of nucleotide substitutions between taxa is surprisingly small for such an ancient disjunction. We were unable to distinguish between historical long distance dispersal or slow substitution rates as the source of this discrepancy. Two of the Retrophyllum species are endemic to New Caledonia; one of these (R. minus) is endangered with less than 2500 individuals remaining in the wild. The other endemic species (R. comptonii) is more widespread. We have used a combination of chloroplast RFLPs and RAPDs to assess the distinctness of these two taxa that can be difficult to distinguish using morphological characters. Both techniques provided taxon-specific markers that allowed the discrimination of the two species and the clarification of uncertain identifications. Within R. comptonii we detected evidence for intra-specific genetic differentiation corresponding to geographical isolation of populations.