Birch polypore

Fomitopsis betulina

''Fomitopsis betulina'', commonly known as the birch polypore, birch bracket, or razor strop, is one of the most common polyporous bracket fungi and, as the name suggests, grows almost exclusively on birch trees. The brackets burst out from the bark of the tree, and these fruiting bodies can last for more than a year.
Birch Polypore - Fomitopsis betulina Fruiting body: fan-shaped; no stem; white pore surface Habitat: Birch https://www.jungledragon.com/image/91664/birch_polypore_-_fomitopsis_betulina.html Birch polypore,Fomitopsis betulina,Geotagged,Summer,United States

Appearance

The fruiting bodies are pale, with a smooth greyish-brown top surface, with the underside a creamy white and with hundreds of pores that contain the spores. The fruiting body has a rubbery texture, becoming corky with age. Wood decayed by the fungus, and cultures of its mycelium, often smell distinctly of green apples. The spores are cylindrical to ellipsoid in shape, and measure 3–6 by 1.5–2 μm.

''F. betulina'' has a bipolar mating system where monokaryons or germinating spores can only mate and form a fertile dikaryon with an individual that possesses a different mating-type factor. There are at least 33 different mating-type factors within the British population of this fungus. These factors are all variants or alleles of a single gene, as opposed to the tetrapolar mating system of some other basidiomycete species, which involves two genes.
Razor Strop Fungus A very young specimen of this fungus growing in a remnant patch of ancient birch forest on Beinn Shieldaig. Birch polypore,Fomitopsis betulina,Razor Strop Fungus,Wester Ross

Habitat

The geographic distribution of ''F. betulina'' appears to be restricted to the Northern Hemisphere. There is some doubt about the ability of isolates from the European continent, North America and the British Isles to interbreed.

It is a necrotrophic parasite on weakened birches, and will cause brown rot and eventually death, being one of the most common fungi visible on dead birches. It is likely that the birch bracket fungus becomes established in small wounds and broken branches and may lie dormant for years, compartmentalised into a small area by the tree's own defence mechanisms, until something occurs to weaken the tree. Fire, drought and suppression by other trees are common causes of such stress.

In most infections there is only one fungal individual present, but occasionally several individuals may be isolated from a single tree, and in these cases it is possible that the birch bracket fungus entered after something else killed the tree. These fungal "individuals" can sometimes be seen if a slice of brown-rotted birch wood is incubated in a plastic bag for several days. This allows the white mycelium of the fungus to grow out of the surface of the wood. If more than one individual dikaryon is present, lines of intraspecific antagonism form as the two individual mycelia interact and repel each other.

The fungus can harbor a large number of species of insects that depend on it for food and as breeding sites. In a large-scale study of over 2600 fruit bodies collected in eastern Canada, 257 species of arthropods, including 172 insects and 59 mites, were found. The fungus is eaten by the caterpillars of the fungus moth ''Nemaxera betulinella''.
Birch Polypore - Fomitopsis betulina An annual birch polypore with kidney-shaped caps that are whitish to brownish with the pore surface being whitish (or brown with age). It's very common on birch trees. The surface of the fruiting body was traditionally used as a strop for sharpening the edges on razors. "Ötzi the Iceman" (the 5,000-year-old mummy found in Tyrol) was found to be carrying this fungus. Birch polypore,Fomitopsis betulina,Geotagged,Spring,United States

Uses

Technically, it is an edible mushroom, with a strong, pleasant "mushroomy" odor but a bitter taste. The velvety cut surface of the fruiting body was traditionally used as a strop for finishing the finest of edges on razors. It is also said to have medicinal properties.

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