Questions: Forest classifications are tools used in research, monitoring, and management. In Finland, the Cajanderian forest site type classification is based on the composition of understory vegetation with the assumption that it reflects in a predictable way the site’s productive value. In Russia, the Sukachevian forest classification is similarly based on understory vegetation but also accounts for tree species, soil wetness, and paludification. Here we ask whether Cajander’s and Sukachev’s forest types are effectively the same in terms of species composition, site productivity, and biodiversity. Location: Boreal forests on mineral soils in Finland and Russian part of Fennoscandia. Methods: We use vegetation and soil survey data to compare the Cajanderian and the Sukachevian systems in terms of the understory community composition (that is supposed to define them), soil fertility and tree productivity (that they are expected to indicate), and biodiversity (that is of interest for conservation purposes). We create and employ class prediction models to divide Russian and Finnish sites into Cajander’s and Sukachev’s types, respectively, based on vegetation composition. We perform cross-comparisons between the two systems by NMDS ordination and statistical tests. Results: Within both systems the site types formed similar, meaningful gradients in terms of the studied variables. Certain site types from the two systems were largely overlapping in community composition and arranged similarly along the fertility gradient and may thus be considered comparable. Conclusions: The Cajanderian and the Sukachevian systems were both developed in the European boreal zone but differ in terms of the exact rules by which site types are determined. Our results show that analogous types between the systems can be identified. These findings aid in endeavors of technology and information transfer between Finnish and Russian forests for the purposes of basic or applied ecological research and forest management.