Each flora is unique. To a greater extent this can be seen in the geographical structure of the differential species of the studied floras. The purpose of the work: to establish the geographical structure of the differential species of the pine forests of the Russian Plain on the southern border of the Pinus sylvestris area for identify the nature and uniqueness of these flora. To achieve the goal, a geographical characteristic has been established for the differential species floras of forest-steppe pine forests Oka-Don lowland: Usmansky and Khrenovsky, and floras of the steppe pine forests of the Trans Volga region: Buzuluksky and Krasnosamarsky. Considering the composition and structure of differential species, it was noted that the nature of each of the compared floras is best reflected in the geographical structure of the aborigine fraction of the floras. The following features were identified. Among the differential species of flora of the forest-steppe forests of the Oka-Don lowland, forest and forest-steppe species with a Holarctic and European- West Asian prevail. Among the differential species of pine forests of the steppe zone of the Trans Volga region, steppe species with a Eurasian and East European-Asian range predominate. Endemic species that were noted in the flora of the all studied pine forests give particular uniqueness.