Chaenotheca ferruginea (Turner & Sm.) Mig.
Thallus covering surface, ecorticate, granular-verrucose, slightly pulvelurent, typically whitish grey, often with limited orange to rusty patches. Apothecia spherical to subconical, 0.5-1 mm diam., on top of 1-3 mm tall spindly stalk, blackish, without pruina. Ascii cylindrical, 8-spored in a raw (seldom in 2 raws) 30-40 x 4-6 µm according to our measures. Ascospores spherical to globose, faint yellow, when mature coarsely and irregularly fissured and then network-like. 7-8 µm. Photobiont : Trebouxia. On pale grey thallus: K- to +/- yellow, on orange patches of thallus : K+ purple. Common (also in cities) but understated due to its small size, on bark of trees (notably conifers) and even on wood of trunks devoid of bark.