Opegrapha viridipruinosa B. J. Coppins & R. Yahr  

Mycobank MB 517715

Thallus thin, grey-green powdery, effuse, turning lemon-yellow in herbarium or almost absent except as thin veil at margins of excipulum. Pigments in thallus dissolving K+ yellow in section (best observed adjacent to or below lirellae). Photobiont trentepohlioid. Lirellae erumpent-sessile, mostly simple, few- or stellate-branched, scattered evenly over the thallus, with thin powdery lateral thalline cover, 0.3–0.6(–1) mm long, 0.1–0.3(–0.4) mm broad. Exciple margins completely carbonized and raised above disc, generally slit-like at first and mostly gaping to broadly exposed later, brownish-yellow at inside margins, K– in section. N+ red. Disc mostly exposed, dark brown and often with green (yellow in herbarium) pruina, dissolving in K to give bright yellow. Hymenium 40–60 µm, I+ red. Ascospores 8/ascus, (3–)4–5 septate, (14)–15–19(–22) x (3–)4–5(–6) µm, hyaline, excluding perispore (1 µm), with medial cells somewhat enlarged, and infrequent slight constriction below these. Perispore of old ascospores turning brown and roughly wrinkled. Pycnidia frequent, pale-green pruinose, sessile 0.07–0.12 mm diam., with short bacilliform conidia 2.5–3 x 1–1.3 µm.