Buellia griseovirens (Turner & Borrer ex. Sm.) Almb.
Thallus crustose, thin, ± rimose-cracked, dull white to pale grey, often surrounded by a grey-black prothallus covered by rounded soralia, crater-shaped or flat with rims slightly prominent, possibly becoming confluent and covering a large thallus fraction, pale green-yellow to pale ash-grey; pale yellow when abraded. Apothecia very rare, 0.5-1 mm diam., disc flat to convex, black. Ascospores, submuriform, grey to brown, 15-30 x 7-13 µm. Photobiont : Chlorococcales. Soralia and thallus : C+/- yellow, K+ yellow later dark red, KC-, Pd+ yellow. Common on ± smooth bark of deciduous trees and shrubs. Often confused with Violella fucata , K+ yellow-brown and Pd+ red-rusty.*