Lepraria caesiella

Lepraria caesiella is a species of leprose lichen in the family Stereocaulaceae. It forms a thin, gray-blue powdery crust composed of granular aggregations and lacks a true cortex or lobes. The species is widespread throughout northeastern North America, occurring primarily on tree bark, especially hardwoods like oaks, though it can also be found on non-calcareous rocks in sheltered locations. It was formally described by Richard C. Harris in 2005 and is characterized by its production of atranorin, zeorin, and pallidic acid. phylogenetics studies have helped distinguish it from the morphologically similar L. harrisiana, which was previously considered part of the same species....read more on Wikipedia.