Molecular markers indicate that the narrow Quebec endemics Rosa rousseauiorum and Rosa williamsii are synonymous with the widespread Rosa blanda

Rosa rousseauiorum Boivin and Rosa williamsii Fern. are two rare roses in eastern Quebec, whose taxonomic status is controversial. Morphological characters alone do not clearly differentiate these two taxa from each other or from the morphologically variable and widespread Rosa blanda Ait. We evaluated the taxonomic status of these two taxa, and of two other R. blanda segregates, Rosa subblanda Rydb. and Rosa johannensis Fern., through an analysis of RAPD, ISSR, and AFLP markers. We surveyed 86 individuals from 36 populations in eastern North America. Despite a high degree of polymorphism, principal coordinate analyses and the weighted pair group method with arithmetic averaging suggest no clustering of individuals that correspond to taxonomic boundaries. However, the closely related Rosa palustris Marsh. is clearly differentiated from the R. blanda s.l. taxa. When populations of R. blanda west of Quebec are included, the principal coordinate analyses and Mantel tests indicate the presence of a significant east-west geographic gradient. Analyses of molecular variation suggest that most of the observed variation occurs within taxa, rather than among taxa. A weak inter-taxon variation is nonetheless significant for RAPD and ISSR data, and a weak pattern dependent on geographical location is evident within the province of Quebec. In accordance with studies based on morphological characters, molecular data indicate that R. rousseauiorum and R. williamsii should not be considered as species distinct from R. blanda.