Ribosomal RNA
This genus of bacteria can form either specific or general symbioses; one species of "Bradyrhizobium" may only be able to nodulate one legume species, whereas other "Bradyrhizobium" species may be able to nodulate several legume species. Ribosomal RNA is highly conserved in this group of microbes, making "Bradyrhizobium" extremely difficult to use as an indicator of species diversity. DNA–DNA hybridizations have been used instead and show more diversity. However, few phenotypic differences are seen, so not many species have been named.