The data of studies and calculations showing the high floristic similarity of the pine forests of the Russian Plain located in the southern part of Pinus sylvestris L. area. Especially high similarity is observed in the indigenous fraction of the flora. The similarity of floras in the adventive fraction is insignificant. Taking into account the forecast of a possible, in the near future, floristic homogenization due to the species of the adventive fraction, we calculated an estimation index,

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... ch indicates an opposite process of homogenization — differentiation. Given the division of advents into groups according to the introduction time, we calculated the estimated index separately for archaeophytes and kenophytes. It was revealed that in pairs of pine forests located relatively close to each other, archaeophytes enhance differentiation, and kenophytes enhance the homogenization of flora. Differential taxa (families, genera, and species) are found only in one of all the studied pine forests, that determine the characteristics of the studied floras. Endemic species have been established that give originality to the flora of the studied pine forests.