Flavoplaca citrina (Hoffm.) Arup, Fröden & Sochting s.l. = Caloplaca citrina (Hoffm.) Th. Fr. (agg.)

    Thallus crustose formed of large scales covered with blastidia becoming yellow soredia and giving a somewhat powdery and granular appearance, the thick and aged thallus are divided into areoles clearly visible in dry weather, yellow to gray-yellow in sunny areas, lemon to yellow -green in less sunny areas, never orange. Apothecia more or less frequent, 0.5 to 1.5 mm in diameter, first submerged then sessile, flat disc then only convex, slightly orange-yellow, lighter margin, sorediate, greenish-yellow. Spores broadly elliptical, polarilocular with a septum 3-5 µm wide and about 1/3 the length of the spore, 10-15 x 5-8 µm. Thallus and apothecia: K+ purple. Photobiont: Trebouxia. Very common species, nitrophilous, not particularly maritime, found on limestone or slightly acidic rocks, but also often on the walls and concrete of structures built along the sea. Species often found with Caloplaca ceracea, Diplotomma alboatrum s. l., Lecanora albescens, Lecanora dispersa, Verrucaria macrostoma, etc.

N.B. Variable and very close to many other maritimes species diversely understand according to different authors. This explains why, in this current presentation, this species is considered as a group of very close species, athough very difficult to discriminate in some cases. Several taxa of this group tentatively are presented here notably  Flavoplaca arcis (not sorediate and sometimes lobate), Flavoplaca flavocitrina of which the thallus has more greenish small sorediate squamules, Flavoplaca limonia with blastidia and on calcareous rocks.