Lecanora barkmaniana  Aptroot & Herk

    Thallus crustose, rather thin, rimose to verrucose, 1-5 cm across, often forming mosaics, pale greyish, white-greyish, surrounded by a greyish prothallus (black prothallus are the ones of contiguous species in case of mosaics), covered with soralia emerging from warts, dispersed at first, but potentially confluent and able to cover the whole thallus surface except prothallus, grey-greenish when moist, yellowish to lemon-yellow when dry. Apothecia very scarce or absent, sessile or immersed below the soredia, 0.4-1 mm diam., disc concave to flat, pale brownish, exciple crenulate, more or less sorediate, whitish, pale grey-yellow (not to be confused with other Lecanora apothecia that may form isolated islets). Ascospores simple, colourless, ellipsoid, 7-10 x 3-4 µm. Photobiont: chlorococcoid. Thallus: C-, KC +/- yellow, K+ yellow, Pd+/- yellow, UV+ pâle orange, K/UV+ bright yellow. On very nutrient-rich substrata and tolerant to air pollution in urban areas, barks of ormental trees, notably within cities, shaded car parks. Not to be confused with other Lecnora species with a more or less yellowish thallus (and not greyish)  as Lecanora compallens always sterile and with negative chemical spot tests. See also Lecanora farinaria which is very similar, with the same chemical reactions but with a thallus more farinose and less verrucose, and with apothecia immersed in much more yellow soredia (whatever the weather) and with a blackish disc. Lecanora expallens is C+ orange ; Lecanora strobilina is Pd+ red-orange. See also Lecanora jamesii of which the thalle is not verrucose and with chemical spot tests negative.