Caloplaca arnoldii (Wedd.) Zahlbr. ex Ginzb. subsp. obliterata

    Thallus crustose, more or less rosette-shaped, 1-2 (3) cm diam., composed of lobes (1-3 mm x 0.5-1 mm) shorter and fan-shaped towards the margin, convex and tightly appressed to the substratum, smooth without pruine, yellow-orange to bright orange, prothallus usually absent or inconspicuous, very thin and yellow on well developed rosette-shaped specimen. Apothecia scarce, adnate to sessile, 0.3-0.8 mm diam., disc flat, orange, exciple rather thin but regular, concolourous to the thallus. Ascospores colourless, ellipsoid, polarilocular, septum wide, about or more than 1/3 of the ascospore length, 8-14 x 4-7 µm. K+ purple. Rare in our prospection area, in the xeric supra littoral zone on well-lit vertical walls of siliceous or weakly acid rocks (microgranites, micaschists...). N.B. This group synonymy is very complex and confusing; we hypothesize that our specimen are related to Caloplaca arnoldii ss. auct. brit. since Caloplaca arnoldii subsp. arnoldii is a southern species thriving on well-lit limestones. See also Caloplaca scopularum which is less orange, larger and forming more regular rosettes and grows on less lit nutrient-rich substrata.