Phaeosphaeria nodorum (synonym and correct taxonomic name: Parastagonospora nodorum) is a major fungal pathogen of wheat (Triticum aestivum), causing the disease Septoria nodorum blotch, and a member of the Dothideomycetes, a large fungal taxon that includes many important plant pathogens affecting all major crop plant families. The Dothideomycetes are a newly recognised major class of filamentous fungi that replaces the long-recognized Loculoascomycetes. It includes the causal organisms of many economically important plant diseases.