The morphological features of Nivatogastrium nubigenum are compared with closely related gastromycetes and lamellate agarics. Only one genus, Pholiota in the Cortinaricaeae, was found to have many features similar to N. nubigenum. The subgenus Flammuloides has many features in common with this gasteromycete.

The fruiting bodies and cultural characteristics of P. decorata, P. scamba, P. spumosa, and P. subangularis are compared with N. nubigenum. All of the fungi studied are found in the western United States on conifer wood. Smooth, brown, thick-walled spores, large cystidia, and a somewhat visicid pileus are found in these species. Thick-walled cystidia, similar to those found in P. decorata, are reported for the first time in N. nubigenum.

Growth rates, oxidase reactions, and morphological features were found to be similar for N. nubigenum, P. decorata. and P. spumosa. Positive oxidase tests, oidia, amorphous refractive bodies, "textura intricata" and inflated hyphal cells were found in these three similar species. Different media were used and additional morphological features were found that can be used to distinguish the species.