Pileus: 3.5 cm - 14.0 cm broad; convex when young becoming plano-convex when mature; margins inrolled at first, then straight and even when mature, at times with flaps of tissue exceeding the tubes; surface dry to moist, rough with appressed fibrils at first then becoming scaly and finally squarrose when mature, often areolate, appearing roughened like stiff velvet; colour evenly vinaceous, dark to reddish violet brown when young, fading to brown to dark brown with age; context 1 - 1.5 cm at junction of stipe, thick, firm, white to pale to pastel yellow, sometimes staining vinaceous brown when bruised; taste mild; odour indistinct.
Tubes: Ascending at first, then notched with a depression appearing free around the stipe; pores are large, 1 mm wide, round to angular especially towards the stipe, greyish yellow to yellowish white, not changing or at times becoming deeper yellow when bruised.
Stipe: 9 - 12 cm X 0.5 - 1.0 cm wide at apex, 1.5 - 4.0 cm wide at base; bulbous at first then becoming equal to tapering upwards to club shaped when mature; surface dry, with long grooves or ridges (striations), at times the apex with reticulations, but soon disappearing, with yellow mycelium at base; dark to reddish brown, often streaked with darker brown black; context firm, solid, colour pallid to pale to pastel yellow with greyish red streaks.
Comments: This species is a common and abundant species in these forests. It is a western hemlock associate, found throughout the Pacific Northwest. It is often found on, though not confined to, coarse woody debris. It is separated from the other 2 boletes in these forests by not changing blue when bruised and having a mild taste. Boletus coniferarum turns blue when bruised and has a very bitter taste. Boletus edulis is separated from B. mirabilis by the colour and texture of the pileus, tubes and stipe.
Arora, D. 1986. Mushrooms Demystified. Ten Speed Press. Berkeley, Ca. pp 958.
Thiers, H.D. 1975. California Mushrooms: A field guide to the Boletes. Hafner Press. pp.261.