Aeciospores of Cronartium flaccidum,C. ribicola and Endocronartium pini show no differences in morphology

The morphology of the aeciospores of the pine stem rust fungi Cronartium flaccidum, Cronartium ribicola and Endocronartium pini, collected from nine locations in Finland, Sweden and Italy, was compared. Surface structures of 900 aeciospores were visually classified using a scanning electron microscope, and dimensions of 1100 aeciospores were measured from micrographs. The data grouping was tested with discriminant analysis. The spores had well-defined smooth areas and annulate warts on their surface. E. pini, C. flaccidum and C. ribicola could not be distinguished by the surface structures of the spores. The grouping of spores by dimensions into sample locations was statistically significant by one discriminant function, while the grouping into species was not. The observed similarities corroborated the current views on the close relationship of C. flaccidum and E. pini.