Summary Formae speciales (ff.spp.) of the fungus Fusarium oxysporum are often polyphyletic within the species complex, making it impossible to identify them on the basis of conserved genes. However, sequences that determine host‐specific pathogenicity may be expected to be similar between strains within the same forma specialis . Whole genome sequencing was performed on strains from five different ff.spp. ( cucumerinum , niveu...