Evolution by Reticulation: European Dogroses Originated by Multiple Hybridization Across the Genus Rosa

The European dogroses (Rosa sect. Caninae (DC.) Ser.) are characterized by a unique meiosis system (‘‘canina-meiosis’’), which controls the heterogamous development of tetraploid egg cells and haploid pollen grains resulting in a pentaploid somatic status. This permanent anorthoploidy is supposed to have originated by a hybridization event in the postglacial period. In this study we present molecular evidence by an analysis of nuclear ribosomal DNA data that dogroses are complex allopolyploids resulting from multiple hybridization events. As previously described, the nrITS-1 region does not undergo concerted evolution in dogroses. Thus, different ITS-1 sequences persist within single individuals. Secondary structure predictions do not point to the existence of pseudogenes within these ITS-1 types. Our data suggest that the pentaploid Caninae genome originated from different members of nondogroses and the now extinct Protocaninae. The genusRosa (Rosaceae) is one of the most important genus of ornamental plants in terms of economy and cultural history of humankind with about 200 species distributed in the Northern Hemisphere (Rehder 1949; Wissemann 2003a). Conventional taxonomy (Wissemann 2003a) divides the genus into four subgenera, three of which are monotypic