Sclerotinia borealis is among the most psychrophilic snow mold pathogen, mainly attacking Poaceae crops such as winter wheat and forage grasses as well as non-Poaceae plants under snow. Isolates were collected through the extensive surveys from North Atlantic islands through European and Asian Russia to Japan. Morphological characterization as well as the effects of temperature and water potential on mycelial growth defined three varieties, i.e., vars. borealis, subarctica, and okhotskana. Phylogenetic analyses based on ITS and EF1-α regions of genomic DNA indicated the monophyly of S. borealis and supported varietal differentiation.