Polyploid and hybrid evolution in roses east of the Rocky Mountains.

This study investigates the impact of hybridization and polyploidy in the evolution of eastern North American roses. We explore these processes in the Rosa carolina complex (section Cinnamomeae), which consists of five diploid and three tetraploid species. To clarify the status and origins of polyploids, a haplotype network (statistical parsimony) of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) nuclear gene was estimated for polyploids of the complex and for diploids of section Cinnamomeae in North America. A genealogical approach helped to decipher the evolutionary history of polyploids from noise created by hybridization, incomplete lineage sorting, and allelic segregation. At the diploid level, species west of the Rocky Mountains are distinct from eastern species. In the east, two groups of diploids were found: one consists of R. blanda and R. woodsii and the other of R. foliolosa, R. nitida, and R. palustris. Only eastern diploids are involved in the origins of the polyploids. Rosa arkansana is derived from the blanda-woodsii group, R. virginiana originated from the foliolosa-nitida-palustris group, and R. carolina is derived from a hybrid between the two diploid groups. The distinct origins of these polyploid taxa support the hypothesis that the three polyploids are separate species.