Lichens marins - Caloplaca arnoldii (Wedd.) Zahlbr. subsp. arnoldiii ss. auct. fr.

Thallus crustose, placodioid forming rosettes of 1-3 cm in diameter, these rosettes being able to organize themselves in large colonies, they are formed of elongated lobes, flat or very slightly convex, with a slightly widened and indented end, surface no or little pruinose, yellow-orange, sometimes a little salmon-pink (if only salmon-pink, see the very similar taxon: Caloplaca clauzadeana), lighter or whitish towards the center but not in a cockade. Apothecia numerous grouped in the center of the thallus, flat to slightly concave disc, dark orange to orange-brown, persistent, thin, paler margin. Long elliptical, colorless, polarilocular spores with equatorial thickening equal to 1/3 of the total length, 8-16 x 3-7 µm. Photobiont: chlorococoid. Thallus and apothecia: K + purple. Relatively common Mediterranean thermophilic species on dry vertical walls of limestone rocks, also on limestone walls. N.B. Species of the Caloplaca saxicola group taken here in the sense of the French authors because there is great confusion in this group which still deserves further research. See Caloplaca saxicola ss. str.. (sometimes synonymized by some authors) with shorter lobes and more powdery or pruinose, less thermophilic and can come on rocks or less calcareous stones. Cf. Caloplaca flavescens much more common with a more yellow thallus and "cockade".