Species in fungi call be defined by reference to species concepts based oil morphology, ecology, biology and phylogenetics. Fusarium graminearum, all important pathogen of wheat, barley, rice and maize has been subjected to analyses based oil all four of these concepts. Data relevant to the biological concept usually are interpreted to support only a single, but genetically diverse, species, while data relevant to the phylogenetic concept usually arc interpreted to support multiple species each with a narrower genetic base. The nomenclature used is important not only for mycologists, but also for regulators and for quarantines that may result from inappropriate applications of the phylogenetic species names. Further work is required to resolve the currently existing incongruities in nomenclature and species concepts.