Genetic diversity in the endangered dysploid larkspur Delphinium bolosii and its close diploid relatives in the series Fissa of the Western Mediterranean area

Allozyme diversity was evaluated in four closely‐related taxa of the Delphinium series Fissa distributed throughout the Western Mediterranean area. All are considered threatened plants. Delphinium bolosii and Delphinium mansanetianum are narrowly endemic to the Eastern Iberian Peninsula, whereas Delphinium fissum ssp. sordidum is found in a few populations across the Peninsula. Delphinium fissum ssp. fissum is more widely distributed but often in small and isolated populations. In this group, Delphinium bolosii is dysploid (2 n  = 18) whereas the other taxa are diploid (2 n  = 16). A total of 12 populations were surveyed, including all known locations for D. bolosii , D. mansanetianum , and D. fissum ssp. sordidum . Eleven enzyme systems were assayed and 15 loci were resolved. Markedly depauperate values for genetic diversity were obtained for D. mansanetianum ( H e  = 0.013) and D. fissum ssp. sordidum ( H e  = 0.044). The estimates for D. fissum ssp. fissum ( H e  = 0.071) were below the values expected for widespread species. Small population size and marginal distribution have probably contributed to the low variability observed in this group. By contrast, D. bolosii exhibited comparatively larger populations and greater genetic diversity ( H e  = 0.138). We suggest that, apart from population size and local adaptation, genetic diversity during speciation may have been promoted by dysploidy through genomic recombination. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 773–784.