Anyone who spends time in the woods in the northern half of North America is likely come across a hoof-shaped fungus growing on the side of a tree or log. One of the most common and widespread hoof fungi is True Tinder Polypore (Fomes fomentarius). It is usually found on birch on a live tree or a standing or fallen dead tree. An individual conk (the hoof-shaped fruiting body) can survive for years, even decades, forming a new ridge or furrow each year.
True Tinder Polypore gets its name from its most common usage, as tinder for starting fires. Otzi the Iceman, the 5,000-year-old mummy found in the Alps in 1991, was carrying four pieces of it.
This species can easily be confused with another birch-loving fungus, False Tinder Fungus (Phellinus igniarius). True Tinder Polypore is distinguished by the lighter, uncracked upper surface of older specimens; whitish margin of actively growing layer and underside; pore tubes that are not layered; and lack of white threads running through the cut flesh.