Arthonia cinnabarina (DC.) Wallbr.

     Thallus crustose, often mosaic-forming, more or less immersed in bark, pale brown-red, pale brown-olive, pale brown-orange, brown-whitish, dull cream, etc., but in general relatively pale, often dotted with minute orange spots, and delimited by a brown prothallus. Apothecia rather numerous, scattered all over the thallus, irregular, roughly rounded or egg-shaped, or more or less angular and polygonal,  surface rough, flat to slightly convex, 0.3-1 x 0.2-0.8 mm, vermilion to brown-red with a vermilion exciple turning brown. This bright colour is often hidden by a white pruine that makes apothecia looking like raspberry macaroons. Ascii utriform, 65-75 x 20-30 µm according to our measures.  Ascospores clavate, oblong-ovoid, (2)-3-5-septate, turning brown when old, 20-28 x 7-10 µm according to literature, 20-30 x 8-10 µm according to our measures. N.B.  Microscope sections of apothecia are characterized by numerous purple elements, notably if they result from old samples - see pictures. Photobiont : Trentepohlia. K+ purple on all orange surfaces. Common near the coast and inland in wet and humid temperate regions, on smooth bark of deciduous trees, visible from quite far. N.B. Very easily confused (notably for old or very red specimen) with Arthonia elegans of which the apothecia are more numerous, linear or stellate and characterized by smaller ascopores, 3-septate. N.B. A great number of varieties belonging to this highly variable species (notably depending on age) has been described.*