ABSTRACTGalls typical ofPeridermium harknessiibut with white aeciospores were found on nativePinus ponderosavar.scopulorumin North Dakota in the same habitat as galls with orange spores. Size and germination characteristics of white and orange spores were similar. Seedling inoculations with white or orange spores and observation of infected trees revealed similar symptom development and virulence levels. Characteristics of cultured isolates derived from white- or orange-spored galls were similar except for color. Isozyme phenotypes of white-spored samples were not significantly different from those of orange-spored samples. These observations indicate that white and orange spore colors are apparently not associated with other measured traits and that the white-spored and orange-spored galls in this stand are phenotypic variants of the pathogen known asP. harknessii.