The evolutionary history of Beringian Smelowskia (Brassicaceae) inferred from combined microsatellite and DNA sequence data

We used the genus Smelowskia, which is distributed in Asia and North America and comprises both diploids and polyploids, as an example to address phylogeny, biogeography and polyploidization in the recently (ca. 3 million years ago) formed arctic biome with particular reference to the Beringian area. We combined data from high-resolution nuclear markers (seven SSR loci) with sequences from two nuclear regions (the low copy RPA2 region and the multicopy nrITS region) and five plastid regions (trnL^UAA and rps16 introns, trnH^GUG-psbA, trnL^UAA-trnF^GAA, and 5′prs12-rpl20 spacers). The different nuclear markers showed a congruent pattern that fits well with that observed in morphology and geography, while the plastid data showed some incongruence. Both sequence and SSR data support merging of Smelowskia porsildii, S. spathulatifolia, and S. jurtzevii into a single species (S. porsildii). An Asian origin of the Beringian taxa was inferred, resulting in two separate lineages of American-Beringian/American taxa. The SSR data confirmed polyploidy in several species, supporting the major role of this process in the evolution of the arctic flora.