Common Name: Birch Polypore. Birch bracket, Birch conk, Razor-strop fungus, Iceman fungus, Kanbatake (Japanese) – The name reflects the characteristic habitat as the birch polypore grows only on birch trees. It has many pores on its lower, spore bearing surface; the name polypore is descriptive of this trait.
Scientific Name: Piptoporus betulinus – The generic name is from the Greek verb piptein which means “to fall” in the sense of failing or cast down and porus, Latin for pores. The species name is from the Latin betula which is the word for birch tree. It is also frequently called Polyporus betulinus
Potpourri: The Birch Polypore is a round to kidney-shaped bracket fungus that grows from a single lateral attachment point on the trunks of birch tress. It has a tough, smooth tan upper surface that cracks and turns grayish with age, an incurved margin, and a white pore surface. It is readily identified as it grows exclusively on birch trees that inhabit the temperate to boreal forests from Siberia in Eurasia to Alaska in North America; it is hence a global species of the northern hemisphere. P. betulinus will grow on other trees but only if they are artificially inoculated, but this is not seen in the natural habitat – it is exclusively a birch fungus.
P. betulinus is primarily saprobic to birch trees, living on dead and decaying boles and fallen branches. It is thought that its spores land on the exposed phloem at a broken branch or other wound and send out tendril-like hyphae to penetrate the trunk so as to eventually form the mycelium of the parent fungus. While the birch tree is alive and healthy, it is able to contain the invading hyphae, but when it is weakened by old age, disease, or other stresses, it can no longer resist and the entire tree is eventually invested. In this sense, the birch polypore is considered weakly parasitic. The fruiting bodies that emerge from the mycelium to spread new spores emerge annually in the spring, though they persist as graying husks for several years (as can be seen in the picture above). The decay process is of the brown rot variety in that the fungus consumes the wood’s white cellulose and leaves the brown lignin behind, a distinct aroma of green apples is often conveyed.
The global reach and ubiquity of the birch polypore did not go unnoticed by indigenous peoples of its native habitats. Over the millennia, trail and error experimentation has resulted in the fungus being used in a number of interesting practical applications. Perhaps the most unusual of these is the etiology of the alternative name of razor-strop fungus. The cap or pileus of the fruiting body has a hard, leathery upper surface. This surface can be peeled off in strips and was used in this form as a strop for sharpening razors and also as a natural emery cloth for polishing metal to achieve an ornamental sheen. A second major functionality is associated with the dense, corky mass of the interior flesh of the fruiting body. Like the Tinder fungus (Fomes fomentarius), the fibrous and sere mass of the Birch fungus was used with a spark producing implement to start a fire at a new campsite. It was also used and as a means to maintain and transport embers from one campsite to another in order to obviate the need to repeat the sometimes difficult fire initiation process. The corky nature of the Birch polypore was also employed in other applications in which absorption was required such as vulnerary dressings, ink blotters, haberdashery sweat bands , and even as a mounting platform for securing the impaling pins used in insect collections.
The Birch polypore is listed as edible in many mushroom field guides, though it is clear that edible and palatable are to be distinguished. According to William Roody’s Mushrooms of West Virginia and the Central Appalachians, it is “edible when young and tender but not often collected due to the bitter flesh.” Charles McIlvaine tersely writes in the 1902 publication One Thousand American Fungi (which is considered by many to be the seminal mycophagous work) that P. betulinus is fair when very young and “unpleasant when old.” He also records that it is eaten by deer. Peintner et al wrote in an article entitled “The Ice Man’s Fungi” in the journal Mycological Research in 1998 that it was common practice for the people of Siberia to knock Birch conks off of trees so that they could be chopped up and eaten while still frozen. The bitterness of the Birch polypore is likely due to the taste imparted by various constituent compounds that make it one of the fungi most noted for their medicinal properties. The ice man provided inconvertible proof that the Birch Polypore was a well known commodity at the dawn of civilization.
Ötzi, who is commonly referred to as the Ice Man, was found in 1991 by Austrian hikers who came upon a frozen corpse half emerged from the Schnalstal Glacier in the Tyrolean Alps. He was exhumed and taken to Innsbruck, Austria for analysis by medical experts. Though it was originally thought that his demise was of relatively recent occurrence, inspection of his artifacts, notably a unique copper hatchet, lead to the conclusion that he was in reality a Neolithic man who had died of presumed exposure about 5,000 years ago. It is fortunate that this fact was determined while he was still frozen, as thawing would have resulted in the deliquescence and putrefaction of his flesh. Ironically, a detailed geographic survey of the site where he was found was conducted in 1998. Ötzi was Italian, which is appropriate, as his name is taken from the Italian sub alpine region of the South Tyrol. He was removed to Bolzano, Italy, where the Archaeological Museum of South Tyrol was built to house his remains. The many artifacts found with him led to a much greater understanding of culture, foodstuffs and tools of early European hominids. Among the artifacts found with Ötzi were two pieces of Birch Polypore threaded on a thong around his neck. It is postulated that he used it as a medicine, as an autopsy revealed that he suffered from parasitic intestinal whipworms (Trichuris trichiura) that cause stomach pain and diarrhea. The Birch Polypore contains numerous compounds that have antimicrobial properties. (Photographs of Oetzi and tinder fungus are from The South Tyrol Museum of Archaeology)
Recent phytochemical analysis of the Birch polypore has resulted in the identification of numerous compounds that have a variety of medicinal implications. These may be broadly described as anti-inflammatory, anti-bacterial, anti-tumor and anti-viral. Six triterpene acids have been isolated that have been shown to have anti-inflammatory properties in the conduct of the “mouse ear inflammation assay” in which a mouse is exposed to a chemical that induces an edema in the ears; the Birch polypore extracts inhibited the formation of ear edemas by between 49 and 86 percent. A compound appropriately named Piptamine (C20H35N3) from the generic name Piptoporus has been isolated which has been shown to have an anti-microbial effect on a number of bacteria including Bacillus subtilus and Escherichia coli. Anti-tumor activity has been demonstrated with extracted polysaccharides which inhibited the growth of sarcoma by 90 percent when injected intraperitoneally (into the peritoneum) into mice at a dosage of 300mg/kg . The eponymous Betulinic Acid extracted from P. betulinus has been found to be toxic to malignant melanoma (skin cancer) cells. It is in the anti-viral properties that the Birch Polypore may have the most potential; extracted nucleic acids have been shown to protect injected mice against a lethal dosage of tick-born encephalitis virus. In his book Mycelium Running, Paul Stamets recounts his having sent mycelial extracts of the Birch Polypore to researchers at the National Institute of Health (NIH) in Bethesda, Maryland where testing revealed that it killed the cowpox virus without harming healthy cells. Stamets filed a patent on the extract on 6 January, 2004 (Pat. No. 60/534,776). He has since filed four continuations of the patent, the latest of which extols the virtues of mushroom extracts in the treatment of viruses including avian influenza, yellow fever and West Nile virus.