Arthonia elegans (Ach.) Almq.

    Thallus thin, most often immersed in the bark, sometimes more or less evanescent, 3-5 cm across, cream orange, yellowish, brown-orange, pale redddish, prothallus paler or with a brownish edging. Apothecia usually very numerous, narrow with pointed apices, most often wavy and linear though occasionally branched or stellate, 0.5-1.5 x 0.1-0.2 mm, brown purple, brown-blackish, blackish, very often surrounded by a bright red pruine, that if well developed may give a red aspect to the thallus. Ascospores colourless when young, brown-black when mature, clavate, with a larger cell at one apex, 12-18 (20) x 4-7 µm. Photobionte : Trentepohlia. Rare (except in some limited sites), on young trees with smooth bark ((Fraxinus, Corylus) in woodlands and oceanic forests. N.B. Very easily confused with Arthonia cinnabarina (notably for old or very red specimen) much more common, and potentially growing on the same substratum, but the latter has less numerous and much larger apothecia, not linear nor stellate and characterized by a polygonal structure of which the center is white due to pruine; in case of uncertainty, a microscope analysis may show longer, narrower ascopores, 3-5-septate.