Format: ORAL

Juliane Rexroth1, Christian Porsche1, Marina Rabarimanarivo2, Stefan Porembski1

1 Department of Botany, Institute of Biosciences, University of Rostock, Germany 2 Missouri Botanical Garden, Madagascar

Inselbergs are isolated, often monolithic rock outcrops, usually consisting of granite or gneiss. They are ecologically separated from the surrounding landscape and are thus referred to as terrestrial islands. Only relatively few plant species possess adaptive traits that enable them to grow successfully in inselberg habitats, characterised by a lack of soil and nutrients. As a typical floristic element of Malagasy inselbergs, the poikilohydric Velloziaceae can be highlighted. To explore the hidden genetic diversity of isolated populations of Malagasy Velloziaceae, which belong to the genusXerophyta,we used microsatellite markers to assess the importance of geographic and ecological isolation on inselbergs as a trigger for speciation. Usually, species of the Xerophyta occur in isolated mats on open rocky slopes. Across all our samples, the analysed loci showed a high genetic diversity. Furthermore, almost all individuals had different multilocus genotypes, excluding clonality. Nevertheless, we were able to identify a few clones in our data. However, the emergence of clones is a relatively rare event. Our previous studies have shown very low gene flow between individual inselbergs regardless of distance, favouring strong genetic and geographic differentiation. The morphological differences between plants from separated localities are probably the result of local adaptations and/or a consequence of phenotypic plasticity. In our analyses, we characterise the genetic diversity of a MalagasyXerophytaspeciestocontribute insights into evolutionary processes that may have led to the diversification of lineages of Malagasy inselberg species and to identify more vulnerable regions that require special conservation measures. Currently, Malagasy inselbergs suffer from human impacts (e.g. quarrying, fire), resulting in a dramatic decrease in the genetic diversity of taxa that consist of small isolated populations. It can be concluded that many spectacular taxa (incl. orchids,Aloespp.) are facing similar problems concerning their long-term survival on Malagasy inselbergs.