Genetic structure and evolution of diploid Cochlearia in Iceland

Within the northern European Cochlearia (Brassicaceae), considerable chromosome variation has taken place without corresponding morphological differentiation, which has resulted in an intricate species complex including two base chromosome numbers and several ploidy levels. Here, we dig into the situation in Iceland. The distribution, genetic structure, taxonomy and origin of the two Cochlearia cytotypes (2n = 12 and 2n = 14) present in Iceland are discussed. Chromosome counts indicate that the 2n = 12 populations are dominating along the coast, whereas only 2n = 14 has been reported for inland alpine populations. RADseq data support geographically structured genetic variation along the Icelandic coast, as well as environmentally structured genetic differentiation between coastal and alpine populations. The alpine populations show genetic and morphological affiliation with C. groenlandica (2n = 14), which is widely distributed in the Arctic, but more comprehensive sampling is needed to conclude on the taxonomical status of the Icelandic coastal plants. To uncover the origin of and phylogenomic relationship among the two chromosome variants, comparative whole-genome sequencing should be performed.