Kennedya yellow mosaic tymovirus (KYMV) occurs along the eastern Australian seaboard in the perennial legumes Desmodium triflorum and D. scorpiurus in the north, and Kennedya rubicunda in the south. The genetic variation of more than 100 isolates of KYMV, most of them from the north, has been studied using an RNA hybrid mismatch polymorphism (RHMP) method. The method clearly separated the isolates into two groups; all the northern Desmodium isolates formed one group and all the Kennedya isolates from the south another. These sub-populations were themselves variable and the Desmodium population alone was more variable than that of the related turnip yellow mosaic tymovirus in the Kosciusko alpine area.