Lecanora gangaleoides Nyl.
Thallus crustose, uneven, verrucose to warted, areolate, areoles convex, greyish tinged green, lower medulla orange visible in case of cortex erosion (orange spots K+ purple), prothallus (or margin) whitish. Apothecia numerous, sessile, to 2 mm diam., disc flat, soon and persistently convex, blackish, exciple determinate, entire, not contorted nor crenulate, whitish. Hymenium section brown-greenish, olive-green. Ascospores simple, ellipsoid, 12-15 x 6-8 µm. Photobiont: Trebouxia. C-, K+ bright yellow, Pd+ yellow to red. Common but highly variable, on siliceous rocks in the xeric supralittoral zone up to the aerohaline zone inland on rocks and stones of walls. N.B. May easily be confused with Tephromela atra which is ubiquist, without specific maritime trends but equally frequent near the seashore. The latter differs (sometimes difficultly) by its thallus whitish to greyish and a black prothallus, by its apothecia with a flat disc and irregular and contorted exciple and by its purple hymenium section. In addition, in the field, Rinodina beccariana Bagl. (thallus tinged green) and Rinodina confragosa (Ach.) Körb. are easy to confuse and observation of bilocular ascospores is required. N.B. In our prospection area, on coastal rocks two other taxa with similar chemical reactions are difficult to distinguih from L. gangaleoides: Lecanora cenisia ss. auct. brit. of which the apothecia disc is brown-reddish although sometimes black and even more confusing, Lecanora praepostera of which the thallus is less verrucose, usually K+ yellow > blood-red and apothecia markedly sessile with a less determinate exciple.*