Abstract <p>Study of genome size variation in cells of vertebrates using DNA flow cytometry makes it possible to determine polyploid individuals precisely, which is extremely important when studying the processes of reticulate speciation. In addition, in many groups of vertebrates, closely related species often differ in the nuclear DNA content. Therefore, the purpose of our study was to explore the variability of genome size and ploidy in populations of 29 species and subspecies of rock lizards of the genus <i>Darevskia</i>, as well as their hybrids. As a result of this study, the range of variability in individuals of different ploidy (91% of diploid and 9% of triploid individuals) was established not to overlap. Among diploid species, no correlation was found between the nuclear DNA content and phylogenetic relationships, geographic coordinates, altitude, average annual temperatures, and precipitation. Representatives of all studied species complexes (with the exception of <i>D. adjarica</i>) had approximately the same limits of variability. Two species (<i>D. derjugini</i> and <i>D. saxicola</i>) show significant intraspecific variability. Comparisons of the genome size of parthenogenetic and bisexual species generally revealed no noticeable differences between them. Studies of triploid hybrids have shown that their genome size as a whole roughly corresponds to the sum of the average size of the diploid genome of the maternal parthenogenetic species and the haploid genome of the paternal species. The variability of genome sizes within samples of triploid hybrids was, on average, slightly higher than in most parthenogenetic species, but somewhat lower than in bisexual species. This paper discusses the peculiarities of reticulate speciation in this group of animals.</p>