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, rather wide and with a thick edge slighty powdery whitish, more or less deformed, black, sometimes, and then typically (but rarely), grooved by several longitudinal furrows, disc hardly visible at the bottom of a narrow slit, 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, délimitant des logettes larges et non lenticulaires, 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), rarely on wood. 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.