Genetic differentiation and speciation in prealpine Cochlearia:: Allohexaploid Cochlearia bavarica Vogt (Brassicaceae) compared to its diploid ancestor Cochlearia pyrenaica DC. in Germany and Austria

Significant geographic partitioning of genetic variation within Cochlearia bavarica was found within populations from Allgau and SE Bavaria (Germany) exhibiting significant genetic differentiation. It has been demonstrated that allohexaploid C. bavarica evolved via hybridization between diploid C. pyrenaica and tetraploid C. officinalis. Presently, only C. pyrenaica is distributed throughout inland Central Europe. It has been concluded that C. bararica is of inter- or postglacial origin, and its speciation was not influenced by human activities. Isozyme analysis revealed that there is a correlation between interpopulational genetic distances and geographic distances among C. bararica populations from both regions, and which is not the case for C. pyrenaica in Germany and Austria. Only high alpine C. excelsa is significantly differentiated among the diploid taxa analysed here. Geographically structured distribution of alleles and their frequencies in C. bavarica populations could not be explained with the distribution of these alleles in C. pyrenaica. The presented findings favour disruption of a former wider distribution area rather than migration of C. bararica or a polytopic origin of this species.