We publish the results of a three-stage study of the floristic heterogeneity of the Melekess-Stavropol physiographic region located on the territory of the Samara and Ulyanovsk Regions. The area belongs to the forest-steppe zone of the Trans Volga Lowland and occupies the area of 7,7 thousand km. Based on the analysis of family spectra, originality of the flora of the region we show the comparison of Soksky and Irgiz physiographic regions of the Samara Trans Volga. At the first stage of the research we consider the internal heterogeneity of the region, changes in the species composition of the flora along a two-sided latitudinal gradient. For this, the course of the curve, reflecting the accumulation of the number of species with an increase in area, has been studied. The accumulation curves of the number of species aligned in both directions showed three stages of an increase in the number of species, indicating the species heterogeneity of the area. The study of the position of the leading families, depending on the size and geographical position of the floristic sample, shows the heterogeneity of the studied Melekess-Stavropol region by the flora type, which is determined by the third term of the first triple of the family spectrum. At the second stage, four floral groups (floristic samples) are analyzed, which are geographically isolated at the first step. A comparison is made of the isolated groupings at the head of the family spectra using the fraction of the family in the flora and the number of species in the family. The third stage includes a comparison of the selected floral groups of the Melekess-Stavropol physio-geographical region according to the Preston index. Taking into account the existing numerical threshold of 0,27, above which the samples should be considered as different floras, it is possible to speak of the presence of four different floras on the territory of the studied area.