Fomes fomentarius

Appearance

"Fomes fomentarius" has a fruit body of between 5 and 45 centimetres across, 3 and 25 cm wide and 2 and 25 cm thick, which attaches broadly to the tree on which the fungus is growing. While typically shaped like a horse's hoof, it can also be more bracket-like with an umbonate attachment to the substrate. The species typically has broad, concentric ridges, with a blunt and rounded margin. The flesh is hard and fibrous, and a cinnamon brown colour. The upper surface is tough, bumpy, hard and woody, varying in colour, usually a light brown or grey. The margin is whitish during periods of growth. The hard crust is from 1 to 2 mm thick, and covers the tough flesh. The underside has round pores of a cream colour when new, maturing to brown, though they darken when handled. The pores are circular, and there are 2–3 per millimetre. The tubes are 2 to 7 mm long and a rusty brown colour.

The colouration and size of the fruit body can vary based on where the specimen has grown. Silvery-white, greyish and nearly black specimens have been known. The darkest fruit bodies were previously classified as "Fomes nigricans", but this is now recognised as a synonym of "Fomes fomentarius". The colour is typically lighter at lower latitudes and altitudes, as well as on fruit bodies in the Northern Hemisphere that grow on the south side of trees. However, studies have concluded that there is no reliable way to differentiate varieties; instead, the phenotypic differences can "be attributed either to different ecotypes or to interactions between the genotype and its environment".

Naming

"Fomes fomentarius" can easily be confused with "Phellinus igniarius", species from the genus "Ganoderma" and "Fomitopsis pinicola". An easy way to differentiate "F. fomentarius" is by adding a drop of potassium hydroxide onto a small piece of the fruit body from the upper surface. The solution will turn a dark blood red if the specimen is "F. fomentarius", due to the presence of the chemical fomentariol.

Distribution

"F. fomentarius" has a circumboreal distribution, being found in both northern and southern Africa, throughout Asia, and Europe, and is frequently encountered. The optimal temperature for the species's growth is between 27 and 30 °C and the maximum is between 34 and 38 °C. "F. fomentarius" typically grows alone, but multiple fruit bodies can sometimes be found upon the same host trunk. The species most typically grows upon hardwoods. In northern areas, it is most common on birch, while, in the south, beech is more typical. In the Mediterranean, oak is the typical host. The species has also been known to grow upon maple, cherry, hickory, lime tree, poplar, willow, alder, hornbeam, sycamore, and even, exceptionally, softwoods, such as conifers.

Uses

The species is not considered edible; the flesh has an acrid taste, with a slightly fruity smell. The fungus has economic significance as it removes any timber value of infected trees. "Fomes fomentarius" infects trees through damaged bark. It will often infect trees already weakened from beech bark disease and thus has the important and useful role of decomposing unusable timber.