Placopsis gelida

Placopsis gelida is a species of saxicolous (rock-dwelling) crustose lichen in the family Trapeliaceae. It forms circular patches on rock surfaces, with a greyish or pinkish body that develops a distinctive cracked, tile-like pattern in the centre and narrow finger-like projections around the edges. The lichen is recognised by its conspicuous reddish-brown, wart-like outgrowths scattered across its surface, which contain additional photosynthetic partners. It reproduces mainly through powdery patches that spread in radiating streaks across the lichen body....read more on Wikipedia.