Placidium arboreum

Placidium arboreum, commonly known as the tree stipplescale, is a species of corticolous (bark-dwelling), squamulose (scaley) lichen in the family Verrucariaceae. Placidium arboreum is primarily found in the southeastern United States, but it also has occurrences in the western and northeastern United States, Mexico, the West Indies, Argentina, and Ontario, Canada. In its habitat, it typically grows at the base of hardwood trees, particularly oak species, and can occasionally be found on other tree genera or even over mosses on limestone. Its preferred substrate is the bark of oak trees, and the lichen usually establishes itself in bark crevices. Originally described as Endocarpon arboreum in 1831, Placidium arboreum underwent various taxonomic changes before acquiring its current generic placement in 2004. Some authors had referred to it as Endocarpon tuckermanii, but the name with the species epithet tuckermanii is now considered synonymous....read more on Wikipedia.