Arctoparmelia

Arctoparmelia is a genus of foliose lichens in the family Parmeliaceae. Established in 1986, the genus comprises five species of rock-dwelling lichens found primarily in arctic and boreal regions of the Northern Hemisphere. These lichens are characterized by their distinctive velvety or ivory-white to pale brown lower surfaces, concentric growth patterns, and unique chemistry, including the presence of alectoronic acid and negative reactions to iodine-based tests. Arctoparmelia species, commonly known as ring lichens, vary in size from small thalli to specimens up to 1 m (3 ft 3 in) in diameter, and typically grow on exposed rocks in cold, dry environments. While most species show broad circumpolar distributions, some are restricted to specific regions....read more on Wikipedia.