Circinaria caesiocinerea
Thallus to 20 cm diam., rather thick, becoming wide-spreading, rimose at the edge to warted-areolate. Areoles 0.3-1(-2) mm diam., continuous, flat or convex, occasionally subsquamulose in the centre of the thallus, irregular to rounded, often uneven with distinct edges and a rough, matt surface, typically pale grey with a blue tinge, becoming dirty dark grey. Prothallus, if present, grey, delimiting.
Anamorph: conidiomata pycnidial, conidia 6-12 × ca 1 μm.
Teleomorph: ascomata apothecia, 0.2-0.8 mm diam., immersed, crater-like, sometimes becoming emergent, well separated. Thalline margin evident from an early stage, thin, entire, somewhat wavy, but rarely prominent. Disc black, shiny, concave, becoming expanded. Asci cylindric-clavate, thin outer coat K/I+ blue, wall and apical dome K/I–, (4-)6-8-spored. Ascospores very variable in size, often poorly developed, 14-30 × 7-16 μm, broadly ellipsoidal, aseptate, hyaline, thin- and smooth-walled, without a gelatinous sheath or epispore.
Chemistry: cortex and medulla K–, Pd– (aspicilin).
Assessed as of Least Concern by Woods & Coppins (2012). Considered to be the most common of the Aspicilia-like fungi on siliceous substrata (Fletcher et al. (2009).
Frequent throughout north and west Great Britain, also throughout southern regions where suitable substrata can be found. Also found throughout Ireland, primarily near the coast.
Found on siliceous rocks, especially by lakes, seashores and nutrient-rich sites such as bird-perching stones, also on walls and memorials.