Lithographa

Lithographa is a genus of lichen-forming fungi in the family Xylographaceae. These rock-dwelling lichens form tightly attached crusts that crack into small tile-like patches, typically appearing in shades of grey, brown, or nearly black. The genus includes six species found primarily in cold regions and high mountains, where they grow on hard rock surfaces in harsh environments. They reproduce through distinctive elongated or round fruiting bodies that appear as dark slits or discs embedded in the crusty surface....read more on Wikipedia.