Melanelixia subargentifera  (Nyl.) O. Blanco & al.

    Thallus foliose, more or less rosette-forming, 4-10 cm across, lobes loosely appressed, 2-6 mm wide, intertwined and partially overlapping, apices upturned and pruinose-like due to minute hyaline to white bristles (observation under magnifying lens), upper surface brown-olive, brownish, greenish, green-brownish sometimes tinged reddish, covered, notably towards the center, with laminal and cortical soralia, more or less dense granulose or verrucose or isidia-like (actual isidia absent), brown-olive, becoming farinose and whitish when eroded (caster sugar-like on rhubarb pie), lower surface matt, blackish with simple rhizines. Apothecia rare, sessile, 1-2 mm diam., exciple sorediate. Ascospores broadly ellipsoid, 11-13 x 7-8,5 µm. Photobiont: trebouxioid. Cortex: C-, K-, KC-, Pd-; medulla and soralia: C+ carmine, K-, KC+ red, Pd-. In theory rather common but to our knowledge not yet found in our prospection area (or mistaken?), on bark of deciduous trees. Not to be confused with Melanelixia subaurifera and Melanelixia fuliginosa subsp. glabratula more tightly appressed and with trues isidia.*