Long known as Bondarzewia mesenterica, and B. montana (Gilbertson & Ryvarden 1986, Siegel & Schwarz 2016, Ginns 2017). Genetic studies (Chen et. al. 2016) showed that the western North American species is distinct from the European B. mesenterica, and it was described as Bondarzewia occidentalis.

Bondarzewia occidentalis is recognized by the large size, growth at the base of (often large) trees or stumps, shelf-like to rosette lobed fruitbody with a brownish, often zonate cap, whitish pores, an acrid to bitter taste, and globose spores with amyloid warts and ridges. It appears to be restricted to old growth forests, or on old growth stumps. Although this species appears to be fairly common in suitable habitat, it appears to be in significant decline, and with the loss of suitable habitat, may warrant it being listed. Many recent observations are from old growth stumps in forests which were logged in the 1960’s and 1970’s. Most of these stumps are becoming too rotted for this species, and a population collapse is expected. 

Bondarzewia occidentalis is restricted western North America from northern California into British Colombia and Alaska.  Mostly associated with old growth Western Hemlock, Douglas Fir, Sitka Spruce, Larix, Fir and other conifers along the coast, Sierra Nevada and Cascade Range, and with scattered records in the northern Rocky Mountains in Idaho.

Currently known from ~600 locations. Mostly fruiting from old growth conifers, or stumps of logged old growth trees. Suitable habitat is highly fragmented and declining. Many recent observations are from old growth stumps in forests which were logged in the 1960’s and 1970’s. Most of these stumps are becoming too rotted for this species, and a population collapse is expected.

Solitary or with a few scattered fruitbodies at the base of old growth trees and stumps of conifers, especially Red Fir (Abies magnifica) and Sitka Spruce (Picea sitchensis) in California, hemlock (Tsuga spp.) larch (Larix spp.), and Douglas-fir (Pseudotsuga menziesii) in the north. Fruitbodies are annual, but can persist for months. Causing white stringy rot of the heartwood of roots and butts of living conifers, continuing to fruit after the tree dies. Also common on legacy stumps in logged old growth stands.

Loss of old growth forest has been highly detrimental to this species, as most fruitings occur on trees of old age and large girth. Although old growth logging has mostly ceased in the lower 48 states, it continues to be cut in British Colombia and coastal Alaska. Stand replacing fires are also highly detrimental, with large swaths of forests being lost to fire in the mountain west.

This species was included in the Northwest Forest Plan as a Survey & Manage speices (as Bondarzewia mesenterica), and targeted surveys have sporadically occurred since 2020. It also has been tracked since 2020, as part of the FUNDIS Rare 20 challenge.

This species has been tracked since 2020, as part of the FUNDIS rare 20 challenge. The data gathered has shown it is still fairly common in suitable habitat, and good baseline data has been established to view trends over the next few years. However, suitable habitat is highly fragmented and declining. Many recent observations are from old growth stumps in forests which were logged in the 1960’s and 1970’s. Most of these stumps are becoming too rotted for this species and we need to track downward trends.

This species is occasionally eaten by humans, but is not held in high regard, and thus, rarely collected.

Chen, J.J., B.K Cui, S.H. He, J.A. Cooper, M.A. Barrett, J.L. Chen, & Y.C. Dai. 2016. Molecular phylogeny and global diversity of the remarkable genus Bondarzewia (Basidiomycota, Russulales). Mycologia 108(4): 697–708.

Gilbertson, R. L., and L. Ryvarden. 1986. North American Polypores. Vol. 1. & Vol. 2. Lubrecht & Cramer Ltd. Port Jervis, NY.

Ginns, J. 2017. Polypores of British Columbia (Fungi: Basidiomycota). Prov. B.C., Victoria, B.C. Tech. Rep. 104. http://www.for.gov.bc.ca/hfd/pubs/Docs/Tr/TR104.htm

Siegel, N. & C. Schwarz. 2016. Mushrooms of the Redwood Coast: A Comprehensive Guide to the Fungi of Coastal Northern California. Ten Speed Press, Emeryville, CA.