The genotypes of phylogenetically homogeneous Rhizobium leguminosarum bacterial strains in nodules of Lathyrus vernus plants were studied. The degree of genetic variation between bacteria within nodules of one L. vernus population correlated with the distance between host plants: the greater the distance, the greater the genetic differences between their microsymbionts. This may be due to the ongoing process of exchanging genetic information between Rhizobium strains, with the depends on the distance between them. But in some cases, this pattern was not observed, and there were significant differences between the microsymbionts of neighboring plants. Most likely, with the exception of spatial limitations, there are some other barriers that exist to the free exchange of genetic information between nodule bacteria.