Summary:
This is a member of the Phellinus igniarius complex according to Zhou, L.-W.(1). Features include 1) flat growth on wood of Betula occidentalis with the dull reddish brown pore surface exposed, 2) a narrow margin that is yellowish brown and tomentose, 3) woody consistency, 4) tight adherence to the wood, 5) round pores, 6-9 per mm with thick edges, 6) indistinctly stratified tubes, and 7) microscopic characters including spores 3.9-4.5 x 2.8-3.6 microns, a dimitic hyphal system, and setae. The description is derived from Ginns(28).
In western North America, Phellinus betulinus is known from BC, WA, ID, and MT (Ginns(28) who notes that the range is uncertain because collections have been mislabeled as Phellinus laevigatus).
Cap:
growing flat on wood with pore surface exposed, widely spread out, "woody, adnate"; margin "yellowish brown, tomentose", up to 0.2cm wide, (Ginns)
Flesh:
up to 0.2cm thick; yellowish brown, (Ginns)
Pores:
6-9 per mm, round, "edges thick, entire", dull reddish brown; tubes "indistinctly stratified", each layer up to 0.1cm deep, paler than flesh
Microscopic:
spores 3.9-4.5 x 2.8-3.6 microns, oval, thin-walled; hyphal system dimitic: generative hyphae 2.0-3.5 microns wide, thin-walled, walls "pale yellow to hyaline", skeletal hyphae 2.5-5.0 microns wide; setae 13.2-18.6 x 5.3-6.8 microns, (Ginns)
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