How diverse can rare species be on the margins of genera distribution?

Different genetic patterns have been demonstrated for narrowly distributed taxa, many of them linking rarity to evolutionary history. Quite a few species in young genera are endemics and have several populations that present low variability, sometimes attributed to geographical isolation or dispersion processes. Assessing the genetic diversity and structure of such species may be important for protecting them and understanding their diversification history. In this study, we used microsatellite markers and plastid sequences to characterize the levels of genetic variation and population structure of two endemic and restricted species that grow in isolated areas on the margin of the distribution of their respective genera. Plastid and nuclear diversities were very low and weakly structured in their populations. Evolutionary scenarios for both species are compatible with open-field expansions during the Pleistocene interglacial periods and genetic variability supports founder effects to explain diversification. At present, both species are suffering from habitat loss and changes in the environment can lead these species towards extinction.