Cap convex 4-12 cm broad, expanding to plano-convex; surface dry, somewhat irregular with scattered bumps and depressions, matted tomentose, frequently partially areolate at maturity; color variable: reddish-brown, maroon, pinkish between cracks in the cuticle, in age often lighter from overlying greyish hairs; context moderately thick, pale yellow, bluing where cut or injured, especially at the junction of the stipe and cap; odor and taste mild.
Pores ochraceous, approximately 1-2 per mm, angular, bluing when bruised; tubes 0.5-1.0 cm long, colored like the pores, depressed at the stipe.
Stipe 4-8 cm long, 1-2.5 cm thick; shape variable: occasionally slender and sinuous, more typically short, straight, equal to ventricose, the base often pinched or flattened; surface nearly glabrous, yellowish at the apex, reddish-brown below from appressed fibrils; context yellow, soft, bluing slowly; veil absent.
Spores 11.5-16 x 5-6.5 µm, elliptical to subfusiform, moderately thick-walled, containing 1-3 vacuoles; spore print brownish.
Solitary, scattered, or in small groups under Quercus agrifolia (coast liveoak); fruiting from fall to late-winter.
Edible, but not choice.
True to its species name, Boletus dryophilus appears to occur only under oak, specifically coast liveoak (Quercus agrifolia). The tomentose cap which often becomes areolate in age, place it in a group with Boletus subtomentosus, and B. chrysenteron. It can be told from these species, however, by its reddish-brown cap (when young), usually short stature, and a tendency to have a narrowed or pinched stipe base.