Seven lineages of Fusarium graminearum were previously identified and recently an eighth was discovered. Lineages are often limited to particular regions of the world.
Stable lineages indicate an historical lack of hybridization.
Some have speculated that each lineage represents a separate fungal species. Long-standing geographic isolation or other reproductive barriers could also explain the presence of such lineages. O'Donnell, K., H.C. Kistler, B.K. Tacke, and H.H. Casper. Gene genealogies reveal global phylogeographic structure and reproductive isolation among lineages of Fusarium graminearum, the fungus causing wheat scab. At least four of these populations contain strains capable of causing FHB on wheat.