Can Crataegus douglasii be found in Québec?

The North American Douglas hawthorn, C. douglasii Lindl., is widespread in the Pacific Northwest, with a disjunct occurrence in the Upper Great Lakes basin. In addition, two Ontario specimens document the occurrence of this species in the Hudson Bay drainage, near Lake Abitibi. Unlike other Ontario hawthorn species (and many Ontario tree species generally) C. douglasii in eastern North America appears to be confined almost entirely to areas in close proximity to shorelines of the upper Great Lakes. Its distribution in Ontario bears little resemblance to that of other plant species that together give rise to the climate- and substrate-controlled ecozones and forest regions in this part of the continent. One hypothesis that has been advanced to explain this difference is the role of periglacial lakes as migration routes from west to east, and the limited ability of black-fruited C. douglasii to expand into the hinterland now occupied by red-fruited hawthorns that, together with many other woody species now dominant, most likely recolonized the Great Lakes basin from refugia in southeastern North America. This poster aims to renew awareness of these biogeographic questions and stimulate botanists to look for hitherto ignored or undiscovered occurrences of Douglas hawthorn in northwestern Québec.