Opegrapha rufescens Pers.
Thallus crustose, very thin, evanescent, more or less smooth and delimited by a brown-blackish prothallus in case of mosaics, olivaceous, brown, grey-brownish, almost with large reddish or ginger areas. Apothecia lirelliform, usually numerous, straight, wavy, branched or slightly stellate, immersed in the thallus, little prominent, 0.3-1 x 0.1-0.2 mm, black, often edged by white dots coresponding to scraps of thallus hyphae, disc opened, distinctly visible, greyish to blackish. Ascospores fili-fusiform, more or less curved, 3-septate, 17-27 x 3-5 µm. Photobiont: Trentepohlia. Chemical spot tests negative. On smooth bark of deciduous trees.*