Rhizocarpon geminatum Körb.  
Family: Rhizocarpaceae
[Lecidea confervoides var. concreta (Ach.) Schaer.,  more]
Rhizocarpon geminatum image
Stephen Sharnoff  
Rhizocarpon geminatum image
Stephen Sharnoff  
Rhizocarpon geminatum image
Stephen Sharnoff  
Rhizocarpon geminatum image
Garry Neil