One hundred and ninety-seven boreal forest stands, in a region of Ontario and Quebec south of James Bay, were examined. Tree species were summarized as relative density of each of five stem size classes. These data formed the basis for an exclusive polythetic divisive stand classification into 10 groups. Most of these groups were characterized by a single tree species. The affinity of each of 410 understorey taxa was assessed with respect to each canopy stand group or natural combination of groups. Only 121 understorey taxa showed specificity to the canopy classes identified. This apparent lack of tight overstorey–understorey affinity is discussed in relation to site nutrient status and regeneration following forest fire.