The Middle Karelia is a territory between the latitudes 63° and 65° North, covering the area of approximately 65 000 km2. Comparative analysis of taxonomic and geographical structures of 15 local floras (LF) located in the Middle Karelia and beyond its bounds has shown that the flora of the Middle Karelia has some distinguishing features, namely the poorness of species composition, undersaturation of the aboriginal fraction, relatively considerable number of alien elements in the flora composition. These features testify to the young age of the flora and continued process of its forming. The conditional character of the boundaries of existing floristic districts and the expediency of the White Sea floristic district restoration have been shown. The approbation of the mathematical methods has revealed their appropriateness for the purposes of floristic zoning.