Cap 7-14 cm broad, convex, expanding to plano-convex; margin decurved when young, level in age, extending beyond the tube layer; surface maroon-brown, to dark reddish-brown, coarsely matted-tomentose to squamulose in age, sometimes with pinkish blotches from the underlying ground color; context 1-2 cm thick, soft, pallid to pale pink, occasionally yellowish, often vinaceous just below the cuticle, unchanging where exposed; odor mild; taste slightly lemon-like.
Pores depressed at the stipe, oval to angular, 1-2/ mm, cream-yellow, maturing yellowish-green, not bruising blue; tubes colored like the pores, pale lemon-yellow, up to 2.5 cm long.
Stipe 7-14 cm long x 2-4 cm in width, narrowed above and enlarged below, the base often clavate; surface colored like the cap, conspicuously reticulate at the apex, the lower portion covered with raised purple-brown fibrils over a pale-pinkish ground color; context fleshy-fibrous, cream-yellow, pinkish at the base, unchanging; veil absent.
Spores 14.0-22.0 x 6.5-8.0 microns, narrowly ellipsoid to subfusoid in both face-view and profile, smooth, thin-walled, hilar appendage conspicuous, one to several organelles present; spores olive-brown in deposit.
Solitary or in small groups, terrestrial or on well-decayed conifer logs and stumps; fruiting shortly after fall rains from Mendocino county northward along the coast; occasional.
Edible and good when free of fly larva.
A striking and beautiful species, Boletus mirabilis is recognized by a maroon to dark reddish-brown, coarsely tomentose to squamulose cap and strongly reticulate to fibrillose stipe. Unusual for a bolete, it often fruits on moss-covered logs and stumps, particularly those of hemlock (Tsuga heterophylla). Boletus mirabilis is unlikely to be mistaken for any other California bolete, but it bears a slight resemblance to the terrestrial polypore Scutiger pes-carpae, known more commonly as Albatrellus pes-carprae. The latter also has a matted tomentose to squamulose cap, which can be brown to maroon. Its stipe, however, is typically eccentric in attachment, and it has a tough, leathery context. Like many boletes, Boletus mirabilis is prone to attack by Hypomyces spp. molds, a factor to consider when collecting for the table.