A frequent destination of mine, as of late, is a wooded trail near my home with a generous quantity of tough tree fungi. One such fungus is Tinder Conk (Fomes fomentarius), a light-colored, hoof-shaped species who I found growing on a Gray Birch (Betula populifolia) tree.
Tinder Conk is a perennial fungus, capable of living for several years if the woody food source allows. According to Greg Marley*, Tinder Conk tends to be smaller on Gray and Paper Birch (B. papyrifera), species who decay rather quickly, and can be longer-lived (and larger) when growing on Silver Birch (B. alleghaniensis), American Beech (Fagus grandifolia), and Maples (Acer spp.). That said, Tinder Conk appears best camouflaged when growing on Paper Birch (bottom photo). To my eyes, the tree and fungus appear meant for each other.
The underside of Tinder Conk is slightly concave and covered with tiny pore openings. It is from these holes that spores are released during periods of active growth. For foragers interested in gathering Tinder Conk for medicine, Greg Marley advises collecting "conks only when they are actively growing and producing spores; in the northeast, that is from June through October." The pore surface, he writes, "should look fresh and evenly buff-tan." So, get to know where this species grows now and return in the summer for prime collection.
Perhaps the most famous use of this shelf fungus is as... Tinder! While I can't speak from experience (though I just added it to my to-try list), I've read that Fomes fomentarius is a superb natural material for catching sparks and creating a smouldering coal.
*To learn more about the medicinal and folk uses of Tinder Conk, I'd recommend Greg Marley's book Mushrooms for Health: Medicinal Secrets of Northeastern Fungi (2009, pages 120-124).