Common Tarcrust
This species forms sheet-like crusts on downed hardwood branches, in this case alder. The stroma often cracks as shown. On its surface are found bumps that are known as perithecia. They are flask-shaped spore-producing vessels with an opening (ostiole) at the apex through which spores emerge. This fungus is an Ascomycete known as a pyronomycete. It adheres tightly to the underlying substrate wood, and is erumpent, meaning it pushes up the bark that overlies it in its spread. It is a frequently encountered species.