Caliciaceae Buellia griseovirens Growth type crustose K+ yellow going red (often weak), C+/- yellow, KC-, P+ yellow, UV- Found on well-lit, +/- smooth bark and worked timber. Can tolerate moderate pollution. Variable. Thallus +/- immersed or thick, greyish with a black prothallus sometimes present. The scattered, crowded or confluent grey-green soralia are often tinged bluish, yellow when abraded or scratched. Apothecia very rare, black discs with brownish epithecium. Spores are irregularly 3-septate to sub-muriform, 15-30 x 7-13 µm. Microscope photograph below. Similar: Mycoblastus fucatus and Mycoblastus caesius

Microscope photograph

Buellia griseovirens
On wood. Studland, Dorset. May 2013. Fertile specimen Kingston Lacy, December 2015