Fomitopsis betulina, long known as Piptoporus betulinus, is a common annual bracket fungus that grows almost exclusively on birch (Betula). It is a necrotrophic parasite of weakened birches and continues as a saprobe on dead trunks, causing a brown cubical rot. The fruit bodies are rubbery when young and become corky with age, with a smooth greyish-brown upper surface and a white pore surface. Specimens were among the items carried by Otzi, the roughly 5,300-year-old Iceman found in the Tyrolean Alps; their purpose is speculative.
Inedible. The flesh is tough, corky and usually bitter; Wikipedia notes it is considered inedible except possibly when young. It is not a food mushroom. It has been used in traditional medicine, and its cut surface was historically used as a strop for razors, as tinder and for mounting insect specimens.
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Mycology is an evolving science: names, classifications and safety information change as research advances. Entries are compiled from cited sources and reviewed, but may be incomplete or out of date — check the sources, and never rely on this library alone to identify or eat a mushroom.
Habitat
On dead and weakened birches (Betula pendula, B. pubescens, B. papyrifera and other birches), on standing trunks and fallen wood. It may lie dormant in wounds until stress such as drought or fire weakens the tree. Fruit bodies are annual but tough, often persisting through winter into the following year.
Distribution
Northern Hemisphere wherever birches grow: widespread and common in Europe, also in Asia and North America; occasionally reported from South America.
Characteristics
Cap: 5-25 cm across, 4-10 cm deep; smooth or slightly roughened; whitish when young, becoming brownish to dull brown; margin thick and rolled over to form a rim around the pore surface. Pores: White, aging grayish to brownish, not bruising; 2-4 per mm; tubes to 1 cm long. Flesh: White, thick, corky, unchanging when cut. Odor: Strong and fragrant when fresh; taste usually slightly bitter. Spores: 4-6 x 1-1.5 um (MushroomExpert; Wikipedia gives 3-6 x 1.5-2 um), allantoid to cylindrical, smooth, hyaline, inamyloid. Key features: On birch only; rounded rim around the white pore surface; corky white flesh.
