A volunteer rye plant ( Secale cereale ) infected by a reticulate spored species of Tilletia was collected in a wheat field in southeastern Idaho in 1993 (WSP 71279). The smut fungus was identified as Tilletia contraversa , the dwarf bunt pathogen of wheat, based on teliospore morphology and stunting of the host. Inoculation studies conducted in the greenhouse confirmed that the rye-infecting bunt was able to infect wheat. A phylogenetic analysis based on the internal transcribed spacer region rDNA, eukaryotic translation elongation factor 1 alpha, and the second largest subunit of RNA polymerase II demonstrated that the rye-infecting bunt was distinct from T. contraversa and the common bunt pathogens of wheat, T. caries and T. laevis . The rye-infecting bunt fits within the species concept of T. secalis , a pathogen of cultivated rye in Europe. The ability of T . contraversa , T. caries and T. laevis to infect rye and of T. secalis to infect wheat has resulted in confusion over the identity of bunts found infecting rye. This study is the first demonstration in North America of a bunt fungus infecting rye that is genetically distinct from the wheat bunt pathogens.