Microsatellites resolve the taxonomy of the polyploid Cardamine digitata aggregate (Brassicaceae)

Polyploidy, probably the single most important mode of sympatric speciation in plants, tends to result in complicated evolutionary patterns. The Cardamine digitata aggregate is a species complex where polyploidy has resulted in taxonomic and nomenclatural controversies. Two basic chromosome numbers are found ( x = 7 and x = 8), and all plants studied so far are tetra‐ to dodecaploids. We used six microsatellite loci originally developed for the Arabidopsis genome to identify evolutionary and taxonomic units within the C. digitata aggregate, obtaining 102 polymorphic markers. Using different analysis methods (PCO, CVA, STRUCTURE, parsimony), we recognised four approximately equidistant units corresponding in morphology with the four described species: C. blaisdellii , C. digitata , C. microphylla , and C. purpurea . All taxa include at least two ploidal levels; thus recurrent taxonomic autopolyploidy is indicated.