Abstract

The assessment of the conservation status of species is crucial to effective conservation strategies, particularly in the current context of global changes. However, the quality of these assessments can be undermined by taxonomic uncertainties. One such case is the black maple whose conservation status is incongruent among Canadian provinces and American states where it naturally occurs. Morphological disparities between sugar maple and black maple led to their description as distinct species at the end of the 19th century, yet extensive hybridization between the two forms and low genetic differentiation has been reported since. The consensus on the taxonomical designation of black maple remains elusive and is sometimes recognised as a subspecies or ecotype of the sugar maple. To further investigate genetic distinctiveness of sugar and black maple, we analyzed high-throughput sequencing data obtained from two 700-meters apart stands within a contiguous forest where the two maples coexist. We sampled groups of individuals presenting the typical morphological characters of limb outlines and pubescence of each maple. Genetic data unveiled substantial differentiation between these two maples, confirming the distinctiveness of the black maple gene pools and justifying its recognition as a distinct species. Furthermore, black maple populations in Quebec exhibited markedly greater genetic structure and inbreeding compared to their sugar maple counterparts at equivalent latitudes. These findings not only affirm the species-level taxonomy of black maple but also represent the first characterization of genetic diversity within populations situated at the northern edge of its distribution range. Its high level of inbreeding is concerning for the conservation of the species in Quebec, and more research is needed to identify its origin.