Common Button Lichen - Buellia erubescens

Buellia erubescens is a crustose lichen with black apothecia that grows on bark and sometimes wood. Buellia is a genus of fungi in the family Caliciaceae. The fungi are usually part of a crustose lichen. In this case, the lichen species is given the same name as the fungus. But members may also grow as parasites on lichens (lichenicolous). The algae in the lichen is always a member of the genus Trebouxia.