Caloplaca flavorubescens (Huds.) J. R. Laundon
Caloplaca aurantiaca auct. p.p. non (Lightf.) Th. Fr.
Thallus crustose, usually effuse, 2-5 cm across, smooth to slightly granular or minutely cracked, lemon-yellow, yellow, grey-yellowish, green-yellow, prothallus invisible or grey-blue. Apothecia usually numerous, 1-2 mm diam., round or slightly distorted, disc flat to slightly convex, bright orange, orange, yellow-orange, exciple distinct, usually persitent, yellow-orange but paler than the disc. Ascospores polarilocular, with a large septum (5-9 µm), 15-18 x 6-10 µm. K+ purple. Rare in our prospection area, on bark of deciduous trees (Fraxinus, Populus, etc.). N.B. Very similar to Caloplaca flavovirescens which is saxicolous and with smaller apothecia.