Graphis elegans (Borrer ex Sm.) Ach.
Thallus very thin, forming coating on bark, smooth to minutely wrinkled, whitish, pale greyish, pale grey-greenish, pale grey-brownish, white-greenish. Apothecia usually in limited numbers, lirelliform, short or elongate, 1-2.5 mm long, straight or curved, seldom branched, black, sides rather wide and thick with typically with several longitudinal furrows, disc persistently slit-like, black (N.B. when falling down, lirellae leave two black strokes on the thallus). Ascospores markedly elongate, fusiform, colourless or slightly dark brown, 10-12-septate, 32-55 x 6-12 µm. Photobiont: Trentepohlia. Thallus : C-, K+ yellow turning red, Pd+ yellow-orange (sometimes faint or hardly visible). Common, oceanic trends, on smooth bark of deciduous trees (notably Betula). See Graphis scripta of which the apothecia are more numerous and the thallus K-. N.B. The typical lirellae, with several longitudinal furrows, sometimes are rare or absent on the same thallus and the best determining marker on the field is the thallus K+ red reaction.*