Buellia ocellata (Flot.) Körb.

   Thallus crustose, up to 2-3 cm diam., forming small patches, areolate, areoles slightly convex, surface rough and uneven, pale yellow-grey, pale yellow, pale grey tinged with yellow-green,  sometimes delimited by a limited black prothallus. Apothecia immersed at first, 0.2-0.5 mm diam., disc concave to flat, black;  true exciple thin, sometimes slightly crenulate or inconspicuous. Ascospores broadly ellipsoid, apices rounded, 1-septate, 11-20 x 7-10 µm. Thallus: C+ orange, K-, Pd-. Photobiont: Chlorococcales. Not especially maritime but not rare on exposed, ± isolated smooth siliceous pebbles and rocks, on the seashore. N.B. Species in general not associated with nutrient-rich substrata, often common on rocks used to delimit car parks along the seashore, associated with other pionner species, notably Rhizocarpon reductum et Buellia aethalea (but the latter is more dependent upon nutrient-rich substratum and prefers enriched rocks) mosaic-forming.  In general, these mosaics are  darker and Buellia ocellata is clearly distinguished by its pale yellowish colour. N.B. Not to be confused with Rhizocarpon geographicum much more bright yellow.