Sagedia

Sagedia is a genus of lichen-forming fungi in the family Megasporaceae. Sagedia species are crustose lichens with immersed, wart-like fruiting bodies that show a depressed disc and a distinct, often raised margin. The genus was established in 1809 by the Swedish lichenologist Erik Acharius and contains 15 recognised species. These lichens grow on rocks or bark and are characterized by a tightly adherent crust that ranges from grey to pale brown, often with faint concentric bands. The genus belongs to a group of related lichens sometimes called the aspicilioid crusts, and its exact boundaries remain debated....read more on Wikipedia.