The thallus is whitish, grey-brown or fawn in colour and immersed in the substrate, often bordered by a brown line. Apothecia up to 0.8 mm in length, irregularly rounded, polygonal or shortly elongate, flat or slightly convex , sometimes disintegrating at the centre, blackish, not pruinose.
Similar in appearance to Arthonia ilicina, but this has ascospores with a muriform "tail" and are distinctly warted when brown. . Also similar to Arthothelium macounii, but this has K+ purplish and magenta pigments in teh epithecium and hypothecium.