Distribution: Widespread in North American coniferous forests, wherever hosts are found: Pinus, Juniperus, Calocedrus.
Habitat: Coniferous forests, wherever hosts are present: Pinus, Juniperus, Calocedrus. Generally inside stumps, at the base of snags or on the undersides of logs.
Substrate: Coniferous wood, rarely hardwoods.
Conservation Status: Not of concern
Differs from Fomitopsis mounceae in thinner, rougher, sulcate cap, sharper margin, and never a red band. Differs from Heterobasidion occidentale primarily by host preference: H. occidentale is found on firs, hemlocks, spruce, and Douglas-fir.
PNW Herbaria: Specimen records of Heterobasidion irregulare in the Consortium of Pacific Northwest Herbaria database
CalPhotos: Heterobasidion irregulare photos