Testing the origins and relationships in the Balkan serpentine endemics in Onosma (Boraginaceae): insights from nrITS sequence data.

Serpentine adaptation is the complex of eco-physiological and morpho-anatomical traits allowing given plant species or populations to tolerate the physical and chemical anomalies of ultramaphic soils, especially the toxic levels of heavy metals (Brooks 1987). Such a capacity originated in a restricted number of species growing obligatedly or facultatively on ultramaphic outcrops. These occur all over the world in the form of ecological islands and are colonized by selected floras with high endemism rates. With ca. 320 endemics, the Balkan ultramaphics represent a major hot-spot of plant diversity and endemism in the Mediterranean (Stefanović et al. 2003). Two angiosperms groups have their centre of diversity in this region, e.g. tribes Alysseae (Brassicaceae) and Lithospermeae (Boraginaceae). Both include endemic lineages at the genus, species and subspecies level, providing the opportunity to study the origin of serpentine endemics at the macro- and micro-evolutionary scale using a phylogenetic approach. A two-markers molecular analysis of Euro-Mediterranean Lithospermeae showed that serpentine specialisation, at least as a facultative condition, originated in three unrelated lineages, among which the Halacsya-Paramoltkia and Onosma-Echium clades. The unexpected sister relationship between Balkan monotypic Halacsya and Paramoltkia shows that obligate serpentinophytism did not originate independently but represents an ecological synapomophy inherited from a common ancestor. In the Onosma-Echium clade, the species-rich genus Onosma include several serpentine endemics, five of which are restricted to the ophiolitic islands of Greece. These taxa represents a model system to investigate whether they represent a monophyletic group with a single origin or a polyphyletic assemblage with multiple origins from non-serpentine, sympatric species. Preliminary results from ITS sequences are revealing complex patterns and a likely polytopic origins through a small number of events, suggesting that potential for serpentine tolerance evolved early in the phylogeny of Onosma as a pre-adaptive trait.