Fomitopsis betulina (previously Piptoporus betulinus), commonly known as the birch polypore, birch bracket, or razor strop, is a common bracket fungus and, as the name suggests, grows almost exclusively on birch trees. The brackets burst out from the bark of the tree, and these fruit bodies can last for more than a year.
Taxonomy
The fungus was originally described by Jean Bulliard in 1788 as Boletus betulinus.
Fomitopsis betulina has a bipolar mating system 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.
Distribution, habitat and ecology
thumb|Variations in size, shape, and surface colour
thumb|Three young fungi on a birch trunk.
Fomitopsis betulina is one of the most common species of brown rot fungi.
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 is eaten by the caterpillars of the fungus moth Nemaxera betulinella. Old fruit bodies that have survived the winter are often colonized by the white to pale yellow fungus Hypocrea pulmonata. except potentially when young.
Research on chemical constituents
Fomitopsis betulina has been widely used in traditional medicines, and has been extensively researched for its phytochemistry and pharmacological activity.
Agaric acid, found in the fruit body of the fungus, is poisonous to the parasitic whipworm Trichuris trichiura. The fungus was carried by "Ötzi the Iceman" — the 5,300 year old mummy found in Tyrol — with speculation that the fungus may have been used as a laxative to expel whipworm.