Caloplaca citrina (Hoffm.) Th. Fr. (agg.)
Thallus crustose, pulverulent, ± entirely granular sorediate, thalli are usually broken up into areoles, yellow in well lit zones, lemon or green-yellow in shaded sections, never orange. Apothecia ± frequent, 0.5-1.5 mm diam., immersed at first, becoming sessile, disc flat somewhat swollen when mature, yellow tinged with orange; thalline margin, paler, granular-sorediate, green-yellow. Ascospores broadly ellipsoid, polarilocular, septum 3-5 µm wide, about 1/ 3 of the length of the ascospore, 10-15 x 5-8 µm. Thallus and apothecia: K+ purple. Photobiont : Trebouxia. Nitrophilic species not especially maritime, occuring on manured or calcareous substrata; limestone, concrete, mortar, cement of various works on the seashore. 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 analysed 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 Caloplaca arcis (not sorediated and and sometimes lobate), Caloplaca flavocitrina of which the thallus has more greenish small sorediate squamules, Caloplaca limonia with blastidia and on calcareous rocks.