PCR/RFLP was used on DNA extracted directly from nodules collected from four species of Casuarinaceae in tropical, North-Eastern Australia and on DNA from reference cultures of Casuarinaceae-infective Frankia strains. PCR products were then analyzed using a set of restriction endonucleases. Five distinct PCR/RFPL groups were recognized on the basis of these restriction patterns. These PCR/RFLP groups were consistently associated with the host-species from which the nodules originated. All isolated reference strains had similar patterns and were allocated to group 1 along with six of the eight unisolated Frankia from Casuarina equisetifolia in Australia. These results demonstrate, that the apparent high homogeneity of Frankia strains in previous studies probably relates to two factors: the single host species from which strains were obtained and, the origin of these strains from areas outside the natural geographic range of the Casuarinaceae. (Texte intégral)