Informative article from Tim MacWelch at Outdoor Life Survival on how to find and use fungi fire starter:
If you have birch or black Locust trees growing near you, then you probably have some very flammable species of fungi also growing nearby.
A classic fire starting tinder of the northeast is the fungus that grows on Birch trees. The species Fomes fomentarius is also known as horse hoof fungus, tinder fungus, tinder conk, and tinder polypore. The species produces fist-sized polypore fruit bodies that are shaped like a horse’s hoof. They vary in color from a silvery gray to almost black, though you’ll usually find them in shades of grey or brown. The dead dry fruiting bodies of this fungus can be shaved into pieces or ground into dust to assist with friction fire spark longevity, or they can be cut into flat chips to be burned as a char cloth substitute in flint-and-steel fire making.
Read more at How to Use Fungi to Start a Fire