This article describes the interaction between a naturally occurring lichen and a modified-bituminous (mod-bit) roof membrane. I have not found this topic discussed by anyone in roofing literature. The growth of this lichen is very slow in relation to the expected life span of a mod-bit roof membrane. As a result, the roof will have reached the end of its useful life and been replaced or been coated or given a cap sheet re-cover before the lichen has advanced to the point of causing a membrane failure. The only routine maintenance that may be required would be patching potholes.