The birch polypore (Piptoporus betulinus) is one of those things in nature that you might see on a regular basis, maybe even every day, and wonder in passing what it is or what it’s called, only to forget about it until it jogs your memory again. There’s not much that seems to stand out about it and it’s probably not something you’d try to remember to describe to your friend at work the next day. But, just because it’s common, it is kind of nice to find out what it is and learn a little something about it, at least I think so.
The birch polypore is a fungus that produces a fleshy, bracket-like fruiting body on the wood of colonized birch trees. It causes a brown rot type of wood decay but only in weakened or dying trees. Once the tree dies, the fungus can continue to thrive on it for some time. The fruiting bodies, the fleshy spore-producing structure, is annual in this fungus and will be produced once the wood in the tree is quite extensively decayed. It’s called a polypore because the lower surface of the fruiting body is made up of many tiny, vertical pores up to about a centimeter high. On the walls of all these pores, spores are produced in late summer through early fall. A single fruiting body will produce millions of spores. Even though these are annual fruiting bodies, producing spores for just a single season, they will darken and stay on the tree for a year or more if undisturbed. An infected tree will often have many brackets, giving them a stepped appearance on the trunk of a still-standing host tree.
The birch polypore is so-named because it is only found on birch trees in nature. It occurs throughout the northern temperate parts of the world wherever birch trees grow. The fruiting bodies or ‘brackets’ are said to have a mild ‘mushroomy’ odor but they are not considered edible. Decayed wood may have a pleasant green apple aroma.
Historically, strips of the leathery brackets have been used by barbers for sharpening their razors or strops and an old common name in some areas is the razor strop fungus. Early man used dried pieces of the fungus to start fires using flint stones and the smoldering fungus could be carried from one site to another then fanned to flame again, serving a very useful purpose in the days before matches and lighters. According to one reference (http://www.first-nature.com/fungi/piptoporus-betulinus.php), there were two pieces of this fungus on a cord around the neck of Ötzi the Iceman, the 5000 year old mummified corpse found by hikers in the Ötztal Alps in 1991. More recently, scientists have extracted an antibiotic, piptamine, from the fruiting bodies. It is not, as far as I can find, currently used in medical treatments or even commercially available.