Lecanora polytropa (Hoffm.) Rabenh.
Thallus rarely continuous and most often formed of areoles scattered on the substrate, particularly in the crevices, areoles with rounded margin, smooth and flat, grey-yellowish, grey-greenish, grey-brownish, more or less obvious black hypothallus. Apothecia numerous, scattered or grouped against each other which has the effect of deforming them, slightly, sessile and constricted at the base, 0.3-1 mm in diameter, disc smooth, flat then slightly convex, pale yellowish, green -brownish, greenish-yellow, jade, thin margin, paler than the disc, distinct then excluded or crenulated or sinuous. Spores simple, elliptical, 10-14 x 5-6.5 µm. Photobiont: Trebouxia. Thallus: C-, weak yellow K+, yellow KC+, P-. Species not especially maritime but very common on acid rocks from the xeric zone, also common on the walls of maritime structures.
N.B. Lecanora stenotropa is a similar species with a darker thallus, brownish disc apothecia and especially narrower spores: 8-12 x 3-4 µm.
N.B. Some forms with a greenish disc can be confused with Lecanora intricata whose areoles have a serrated margin and whose apothecia are less sessile, but these two species are sometimes impossible to separate because of the unreliable characters and crosses selected to determine them.