Lecanora farinaria Borrer

    Thallus crustose, rather thin, finely areolate, areoles contiguous, more or less smooth, pale grey-whitish, sometimes pale dull yellowish, prothallus inconspicuous, sometimes visible, black, thallus covered with soredia, in small mounds, potentially coalescing to cover the whole thallus, yellow to pale yellowish. Apothecia rare, 0.5-1 mm diam., scattered, innate becoming erumpent, discs brown-blackish to blackish, exciple thick and markedly sorediate, concolourous to the thallus. Ascospores colourless, simple, very broadly ellipsoid, 14-17 x 7-15 µm. Thallus and soralia: C-, K+ yellow, KC +/- yellow, Pd-. Rare, on dead wood but also on tree barks at the edge of rivers or lakes (Salix, Platanus x acerifolia). Not to be confused with Lecanora barkmaniana which is very similar including chemical reactions, but a more verrucose thallus and less yellow soralia (the two species, when sterile,  are indistinguishable unless a full chemical analysis is conducted; this explains why we have added Cf. ). See also Lecanora jamesii which is rather similar but whith negative chemical reactions.