Phylogeny and biogeography of wild roses with specific attention to polyploids.

BACKGROUND AND AIMS The genus Rosa (150-200 species) is widely distributed throughout temperate and sub-tropical habitats from the northern hemisphere to tropical Asia, with only one tropical African species. In order to better understand the evolution of roses, this study examines infrageneric relationships with respect to conventional taxonomy, considers the extent of allopolyploidization and infers macroevolutionary processes that have led to the current distribution of the genus. METHODS Phylogenetic relationships among 101 species of the genus Rosa were reconstructed using sequences from the plastid psbA-trnH spacer, trnL intron, trnL-F spacer, trnS-G spacer and trnG intron, as well as from nuclear glyceraldehyde 3-phosphate dehydrogenase (GAPDH), which was used to identify putative allopolyploids and infer their possible origins. Chloroplast phylogeny was used to estimate divergence times and reconstruct ancestral areas. KEY RESULTS Most subgenera and sections defined by traditional taxonomy are not monophyletic. However, several clades are partly consistent with currently recognized sections. Allopolyploidy seems to have played an important role in stabilizing intersectional hybrids. Biogeographic analyses suggest that Asia played a central role as a genetic reservoir in the evolution of the genus Rosa. CONCLUSIONS The ancestral area reconstruction suggests that despite an early presence on the American continent, most extant American species are the results of a later re-colonization from Asia, probably through the Bering Land Bridge. The results suggest more recent exchanges between Asia and western North America than with eastern North America. The current distribution of roses from the Synstylae lineage in Europe is probably the result of a migration from Asia approx. 30 million years ago, after the closure of the Turgai strait. Directions for a new sectional classification of the genus Rosa are proposed, and the analyses provide an evolutionary framework for future studies on this notoriously difficult genus.