Cap 7-12 cm broad, convex, expanding to plano-convex; margin decurved becoming nearly plane at maturity; surface dark-brown, dull, matted tomentose, in age blackish-brown, sometimes patchy-areolate; context 1.0-1.5 cm thick, soft, whitish, unchanging or slowly pinkish-tan to pale blue; odor and taste "fungal."
Pores 1-2 per mm when young, approximately 1 per mm at maturity, angular, at first dingy light-brown, medium-brown in age, sometimes bluing where bruised; tubes, up to 1.5 cm long, concolorous with the pores, depressed at the stipe.
Stipe 7-15 cm long, 1.5-3.0 cm thick, solid, equal to tapering to an enlarged base; surface fibrillose-striate, the fibrils blackish-brown over a pallid ground color, darker where handled, sometimes pinkish where bruised, then blackish-brown; context fleshy, white, the upper portion when cut, slowly greyish, then blackish-grey, the base when cut turning pinkish-tan, then dark-grey; exterior of stipe base whitish, often well rooted in the substrate; partial veil absent.
Spores 14.5-17.0 x 6.0-7.5 µm, smooth, thick-walled, ellipsoid to subfusoid, 1-3 guttulate, hilar appendage inconspicuous; spore print reddish-brown.
Solitary to scattered under conifers, especially Sitka Spruce (Picea sitchensis); fairly common from Mendocino Co. north along the California coast; fruiting from late fall to mid-winter. Less common south of Mendocino, usually associated with pines.
Experience is limited, but it is probably edible.
Tylopilus porphyrosporus is one of California's more distinctive boletes with a dark-brown to almost blackish color. It is also the Tylopilus species most likely to be encountered, at least along California's north coast. Tylopilus indecisus is similar, but is lighter-colored and has a conspicuously reticulate stipe. An unusual aspect of Tylopilus porphyrosporus is the color changes it exhibits when cut or bruised. These typically are slow to develop and usually involve an initial change from cream to pale pink, then greyish-black, or in some cases, at first pale blue, then greyish-black. This species often stains wax paper collecting bags blue.