Fomitopsis betulina (formerly known as Piptoporus betulinus) is more  commonly known as the birch polypore or razor strop fungus. It is is a bracket fungus that primarily grows on birch trees. Characterized by its hoof-like appearance, this fungus has a smooth, creamy to pale brown upper surface and a white to pale brown porous underside. The fruiting bodies are perennial and can range from 5 to 20 cm in width. Its texture is tough and leathery when fresh but becomes brittle upon drying.

This fungus plays a significant role in the decomposition of dead birch trees, aiding in nutrient recycling within forest ecosystems. It is a saprophytic fungus, meaning it feeds on dead organic matter, particularly wood. Piptoporus betulinus can cause a brown rot, breaking down cellulose and leaving behind the lignin, which contributes to the structural degradation of the host tree.

Microscopically, it features cylindrical spores and a monomitic hyphal system, meaning its fruiting body consists solely of generative hyphae. These spores are released through the pores on the underside of the bracket, spreading to new locations to continue the life cycle.