Hybridization between the locally endangered Rosa spinosissima and Rosa mollis results in the pentaploid Rosa ×sabinii in western Norway

Rosa spinosissima is an endangered species in Norway, found only within a limited area on the southwestern coast. Presumed hybrid forms between R. spinosissima and rose species within R. sect. Caninae have been recorded from this area since the late 19th century. Here, analyses of such hybrid plants and selected populations of the tentative parent species were performed using AFLP markers, nuclear DNA content, pollen viability and seed germination rates, in addition to classic morphometric analysis. It is established that the hybrid rose represents a single hybrid taxon, viz Rosa × sabinii, formed by recurrent asymmetrical hybridization events between R. spinosissima and R. mollis, with the latter being the obligate ovule donor. The evidence presented does not indicate hybridization with other co‐occurring rose species, or of introgression from R. mollis into R. spinosissima through backcrossing with R. ×sabinii.