Verrucaria bulgarica

Verrucaria bulgarica is a species of crustose lichen in the family Verrucariaceae. It forms a very thin, brown crustose thallus on soft limestone rocks, breaking into small angular plates dotted with minute, low-domed fruiting bodies. Originally described in 1930 from the Rhodope Mountains of Bulgaria, the species is now known from a handful of widely scattered locations including Great Britain and the South Orkney Islands in the Southern Ocean. The lichen is considered rare and is distinguished by its reduced structure, simple ascospores, and preference for calcareous substrates in cool, humid conditions....read more on Wikipedia.