Lecanora jamesii J. R. Laundon

    Thallus crustose, usually determinate, circular or oval, 1-4 cm across, thin, smooth to minutely granular, greyish, grey-greenish, grey-yellowish, typically with almost transluscent sections, greyish when moist and with sections covered with calcium oxalate crystals (marble aspect of frozen water surfaces), covered with conspicuous and distinct hemispherical soralia, 1-2 mm diam., whitish to yellowish in dry weather and greenish in wet weather, prothallus thin, fibrous, concolourous although most often blackish in case of mosaics. Apothecia very scarce, most often absent, but in our prospection area some sites frequently may harbour fertile specimen, 0.5-1 mm diam., innate then sessile, disc flat, reddish, brown-pink or blackish, exciple covered with whitish crystals, minutely crenulate, becoming excluded (resemble those of Lecanora chlarotera with a sorediate margin). Ascospores simple, ellipsoid, 10-14 x 6-8 µm. Photobiont: Trebouxia. Thallus: C-, K-, KC-, Pd-; soralia: KC+/- yellow. Rare, mostly found on smooth bark of deciduous trees, notably Salix, Fraxinus and Alnus, in very humid areas in hyperoceanic forests, very rare on weakly acidic rocks but see: Lecanora jamesii forme saxicole.

_ Not to be confused with Lecanora barkmaniana which is rather similar but of which the thallus is verrucose and K+ yellow, and with Loxospora elatina of which the soralia are greener, potentially confluent and the thallus is K+ yellow and Pd+ orange.