Oak mazegill

The sessile, fan-shaped fruiting bodies are typically 3–20 centimetres (1–8 in) wide and up to 8 cm thick. They are found singly or in tiered groups, usually on rotting oak. The upper surface of the cap may be various shades of brown, and is sometimes zonate. The pore surface, white to tan in color, is initially porous, but as the fruit body matures, some of the pore walls break down, forming slits with blunt partitions. This results in the characteristic maze-like (daedaloid or labyrinthinine/labyrinthiform) appearance. The tube walls are 10–30 mm (0.39–1.18 in) long, with thick walls. The basidiospores are 5–7 × 2–4 μm, smooth, and elliptical in shape. In deposit the spores are white. A variant has been described that has large, angular pores similar to those in the genus Trametes, named F. quercina forma trametea.

Although Fomitopsis quercina prefers to grow on Quercus species, it has also been found on the tree species Fagus grandifolia, Fraxinus americana, Juglans nigra, and Ulmus americana. It has been reported from nearly all European countries, following the pattern of oak distribution. It has also been reported in Northern Africa, North America, (Tunisia), Asia from Caucasus to India, and also Australia.

The fruit bodies have been used as a natural comb and aphrodisiac, employed for brushing down horses with tender skin. Gilbertson notes that in England, smoldering fruit bodies were used for anesthetizing bees. This species has been investigated for application in bioremediation. The lignin-degrading enzyme laccase, isolated and purified from F. quercina, has shown use in biodegrading a variety of toxic dyes and pigments. The compound quercinol (a chromene derivative), isolated from the oak mazegill, has anti-inflammatory activity, and inhibits the enzymes cyclooxygenase-2, xanthine oxidase, and horseradish peroxidase. The mushroom is inedible due to its toughness.