A common lichen of smooth acidic bark in the south and west, but absent from polluted areas. Very distinct when mature from the striate (grooved) back exciple and the K+ yellow→red (crystals) spot test, but younger material lacks the groves and the norstictic acid can be week or patchy. Also with the newly elucidated additional Graphis species, two others also have striate exciples: Graphis chlorotica and Graphis leptoclada, but these lack norstictic acid. Absolutely definitive, however, are the thick walled spores, which are unlike any other British Graphis.
Thallus smooth and thin or uneven to cracked, ± glossy, continuous, pale to dark grey with a yellowish-orange tinge when fresh. Apothecia unbranched or branched, short or elongate, straight or curved; true exciple black, 5–20 × 2–4 mm, each side with 1–6 longitudinal furrows, disc persistently slit-like; orange stains in the thallus and sometimes old apothecia K+ purple. Ascospores 32–55 × 6–12 µm, (8–) 10–12-septate, fusiform-cylindrical with distinctive thick walls. Thallus C–, K+ yellow→red (crystals), Pd+ yellow becoming orange (reactions often patchy), UV– (norstictic acid).
Very variable and young specimens without furrows in the exciple can be distinguished from G. scripta s. lat. by the K+ yellow→red reaction, although this can be week or patchy. The distinctive thick spore walls, however, readily seperate this species from other Graphis species. Thalli should be carefully examined for the small (0.3–1.5 × 0.2–0.5 mm), generally unbranched apothecia of Melaspileopsis diplasiospora.
On moderately smooth, slightly shaded and usually acidic bark on a wide range of trees, usually in woods, rarely on shaded siliceous rocks; frequent.
Throughout oceanic Britain and Ireland but absent from large parts of C. England due to pollution, a relict in ancient woodlands of the Midlands. Naturally rare in the sub-oceanic areas of north east Scoatland.
Aptroot, A., Weerakoon, G., Cannon, P., Coppins, B., Sanderson, N. & Simkin, J. (2023). Ostropales: Graphidaceae, including the genera Allographa, Clandestinotrema, Crutarndina, Diploschistes, Fissurina, Graphis, Leucodecton, Phaeographis, Schizotrema, Thelotrema and Topeliopsis. Revisions of British and Irish Lichens 36: 1-23.
Text by Neil A Sanderson based on Aptroot et al (2023)