Fruiting annual, solitary to clustered, fan-shaped or convex, sometimes centrally depressed; margin entire to irregular; surface short pubescent, occasionally furrowed, lilac-brown, grey-brown, to dark-brown; context 0.7-1.5 cm thick, white, fleshy, tough, unchanging; odor mild; taste bitter, often latently bitter.
Pores white to cream, 1-2 per mm, thin-walled, angular at maturity. Tubes 0.3-0.7 cm long, white, decurrent.
Stipe 4-9 cm long, 2-3.5 cm thick, usually laterally attached, solid, tough, usually tapering downward and extending into the substrate, the radicating portion white with adhering debris; elsewhere the stipe surface like the cap, i.e. dull brown and pubescent.
Spores 10.5-14.0 x 4-5 µm, spindle-shaped, nonamyloid, smooth to roughened; spore print white.
Solitary to clustered on ground, sometimes at the base of conifer stumps, trees, or on buried wood; fruiting during the middle of the mushroom season, usually late November through December.
Inedible; tough and bitter.
Jahnoporus hirtus is a tough, bitter tasting, ground-dwelling polypore recognized by a grey-brown, finely pubescent cap and eccentric stipe usually well-rooted in the substrate. Additionally, it has relatively small, white pores and non-amyloid, spindle-shaped spores. Though not abundant, it is found in our area every year. Bondarzewia montana is similar when fruiting singly, but has larger pores, lacks a distinct stipe (the cap gradually merges into the stipe), is slightly sour, not bitter in taste, and the spores are round, with amyloid ornamentation. Several Albatrellus species also resemble Jahnoporus hirtus, but only A. pescaprae is likely to be confused with it. The latter is distinguished by a brown to mahogany-brown, more conspicuously pubescent cap, larger white to cream colored pores, and the stipe is neither grey/brown or pubescent. Microscopically, it can also be told apart by smooth, elliptical spores that are 4.5-9 x 5-6 µm. Note, our spore measurements for Jahnoporus hirtus are smaller than reported by Gilbertson (12.5-17 x 4.5-5.5 µm) but we have checked only a few collections.