Lecanora chlarotera subsp. chlarotera Nyl. forma chlarotera
Thallus crustose which can reach 3-12 cm in its greatest length, relatively thick, granular to warty, light gray, greenish-gray, no hypothallus (do not confuse with that of a adjacent species!). Apothecia numerous and sometimes close together, 0.5-1.5 mm in diameter, sessile, flat then slightly convex disc, brown, reddish-brown, orange-brown, ochraceous-brown, with greenish tones when moist, thin margin, persistent, concolor to the thallus, smooth or sometimes a little crenate and convoluted (if the margin is strongly crenate see: Lecanora chlarotera subsp. chlarotera forma rugosella), a section examined under a polarizing microscope shows large crystals not soluble in KOH, granular epithecium with a thin layer of crystals soluble in KOH and not infiltrating between the paraphyses (if this is the case see Lecanora hybocarpa ss. auct. brit.). Simple, largely elliptical spores, 11-14 x 6-7 µm according to the literature, 9-15 x 6-8 µm according to our measurements. Photobiont: Trebouxia. Thallus: C-, K+ yellow, KC-, P-. Common but very variable species found on the bark of trunks or large branches of deciduous trees, particularly street or garden trees, very rarely on wood.
_ Very similar to Lecanora hybocarpa ss. auct. brit. which can only be separated by examining a section of apothecia in polarized light and which shows an epithecium whose small crystals infiltrate between the paraphyses (like roots!).
N.B. many subsp., varieties and forms have been described, see for example:
_ Lecanora chlarotera subsp. chlarotera forma rugosella, whose apothecia have a strongly crenate margin.
_ Lecanora chlarotera subsp. meridionalis (H. Magnus.) Clauzade & Cl. Roux whose apothecia are black-brown to black.
_ Very easily confuse with Lecanora argentata which in principle has a blackish hypothallus and scarse apothecia but a microscopic examination of an apothecia section is often necessary to separate the two species.
N.B. The apothecia of this species are often parasitized in the form of small black dots by Vouauxiella lichenicola.