Lepraria incana  

Thallus diffuse, pale to usually dull blue- or green-grey, occasionally with dull pale orange patches, granules 50-120 µm diam. (rarely to ca 200 µm at the margins), projecting hyphae usually absent or very short, giving a fairly firm appearance to the granules. Medulla absent.
Anamorph and teleomorph: not known.
Chemistry: thallus C–, K–, Pd–, UV+ bluish white (divaricatic and nordivaricatic acids [trace], zeorin), frequently also containing parietin, often irregularly distributed in the thallus and then K+ purple, UV+ pale orange.