The genus was circumscribed by Finnish mycologist Petter Karsten in 1881 with Fomitopsis pinicola as the type species.

[2] Molecular analysis indicates that Fomitopsis belongs to the antrodia clade, which contains about 70 percent of brown-rot fungi.

[6] The generic name combines the name Fomes with the Ancient Greek word ὄψις ("appearance").

Microscopically, Fomitopsis has a dimitic hyphal system with clamped generative hyphae.

The spores are hyaline, thin-walled, smooth, roughly spherical to cylindrical, and are negative in Melzer's reagent.