Arthothelium taediosum

Many times the apothecia of both Arthonia and Arthothelium are very thin or so irregular that a good thin section is hard to obtain. The exciple is usually totally absent in these genera and other parts are often hard to detect. Thin sections of A. taediosum have a distinct brownish tone. The epihymenium is dark brown and the hypothecium is poorly developed and hardly distinguishable.