A woody polypore on dead hardwoods with a maze-like underside. Cap is 4 to 20 cm; broadly convex to more or less flat; fan-shaped in outline; dry; smooth or finely fuzzy (generally smoother toward the margin); whitish when fresh, but grayish, brown, or black in age. Undersurface is maze-like, with thick walls (about 1 to 3 mm wide); occasionally developing pore-like or gill-like areas; whitish when fresh, becoming dingy yellowish or pale tan; not bruising. Stem is absent. Flesh is whitish, or with age brownish; very tough. Potassium hydroxide reaction turns all parts dark grey to black.
Typically found on decaying hardwoods, especially oak.