Eight species of the Botryosphaeriaceae (canker and dieback pathogens) were identified on native Syzygium cordatum in South Africa, based on anamorph morphology, ITS rDNA sequence data and PCR-RFLP analysis. The species identified were Neofusicoccum parvum, N. ribis, N. luteum, N. australe, N. mangiferae, Botryosphaeria dothidea, Lasiodiplodia gonubiensis and L. theobromae. Their pathogenicity on S. cordatum seedlings and a Eucalyptus grandis × camaldulensis clone was determined in glasshouse inoculation trials. Isolates of all identified species, except one of N. mangiferae, were more pathogenic on the Eucalyptus clone than on S. cordatum. Some of the species that cross-infected these hosts, such as N. ribis, N. parvum and L. theobromae, were amongst the most pathogenic on the Eucalyptus clone, while B. dothidea and L. gonubiensis were the least pathogenic. Results of this study illustrate that species of the Botryosphaeriaceae from native hosts could pose a threat to introduced Eucalyptus spp., and vice versa.