Oak Crust

Peniophora quercina is a species of wood-decay fungus in the family Peniophoraceae. It produces fruit bodies that vary in appearance depending on whether they are wet or dry. The wet fruit bodies are waxy and lilac, and attached strongly to the wood on which they grow. When dry, the edges curl up and reveal the dark underside, while the surface becomes crusty and pink. P. quercina is the type species of the genus Peniophora, with the species being reclassified as a member of the genus upon the latter's creation by Mordecai Cubitt Cooke. P. quercina is found primarily in Europe, where it can be encountered all year. Though primarily growing upon dead wood, especially oak, it is also capable of growing upon still-living wood.

Excerpt from the Wikipedia article Peniophora quercina, by its authors, under the CC BY-SA 4.0 licence.