Some test have shown Typhula idahoensis to be interfertile, or not to be; and there are significant morphological and range differences; and so it is sometimes regarded as a subspecies or non-synonymous entirely.

Another proposal divides the worldwide population into two species, I and II, based on morphology and interfertility: I including Japanese A above, North American ishikariensis and idahoensis, and Norwegian I and III, with hosts monocots, dicots, conifer seedlings, and in Russia the roots of hops; II including Japanese B, North American canadiensis, and Norwegian II, only harming monocots.

Genetic factors governing sclerotial size vary widely across the world, and differences between Japanese B and Polish populations have been studied and are pronounced.

It is broadly agreed that there is some degree of differentiation within the species along the lines of winter weather in the various locales.

[1] Does not grow well on lower-water potato dextrose agar, unlike some snow moulds (such as Sclerotinia borealis which is more adapted to continue parasitizing plant tissues in frozen soil).

[1] Low amounts of sclerotinial proteins do occur in the vegetative hyphae - whether produced there or progressing into there - during normal growth at 5 °C (41 °F).

Genetic factors governing sclerotial size vary widely across the world: Specifically in Japanese B, long snowcover selects for larger, and brief snowcover for smaller; while in Polish populations, incubation temp was significant and overwhelmed genetic factors, more often producing smaller sclerotia.

Across the world, smaller sclerotia are an adaptation to shorter or highly variable duration of snow cover, and strongly for the combination of the two.