Athallia pyracea

About

Athallia pyracea is a species of crustose lichen in the family Teloschistaceae. It forms a very thin, often inconspicuous greyish crust on bark, with scattered to crowded orange fruiting bodies typically 0.3–1.0 mm across. The species grows mainly on the nutrient-enriched bark of deciduous trees such as aspen, poplar, and ash and is considered a nitrophilous (nitrogen-loving) lichen. It is widespread in temperate regions of the Northern Hemisphere, occurring across Europe, North America, and parts of Asia. The yellow and orange parts of the thallus and apothecia turn purple when treated with potassium hydroxide. The species was transferred to Athallia in 2013 as part of a molecular reclassification of the Teloschistaceae.

Summary from Wikipedia