Ochrolechia tartarea

Ochrolechia tartarea is a species of saxicolous (rock-dwelling) crustose lichen in the family Ochrolechiaceae. It forms thick, greyish crusts with a rough, crumbly surface marked by irregular warts, typically found on acidic rocks in moist, upland environments across Europe and parts of Asia. The lichen produces distinctive reproductive structures (apothecia) that appear as rounded, pale brown to orange-pink discs up to 5 mm across, often densely packed across its surface. Originally described by Carl Linnaeus in 1753 as Lichen tartareus, it was historically significant as the source of cudbear, a red dye that was commercially important in 18th-century Scotland before overharvesting led to population declines. The species is widespread in the oceanic and mountainous regions of Britain and Ireland, extends through the Alps of central Europe, and has been recorded as far east as South Korea, though it becomes rare in lowland areas and is often confused with similar species....read more on Wikipedia.