Draft
Thallus granular, grey. Apothecia 0·6–1 mm tall, normally 3–5 times as high as the width of the stalk, black, I–, a very thin outermost layer I+ blue; yellow pruina present on head and exciple margin; head 0.3–0.6 mm diam., broadly lenticular; stalk 0.1–0.3 mm diam. Asci clavate-cylindrical. Ascospores 13–16 × 5.5–6.5 µm, with helically arranged ridges. Thallus K+ yellow→red, Pd+ yellow-red (norstictic acid); the pruina contains vulpinic acid.
Characterised by the yellow pruina which is best developed on the heads of young apothecia. In C. trabinellum the yellow pruina is restricted to the lower surface of the head.
On dry, old Quercus bark, with all 20th and 21st century records form ancient deer parks or old growth pasture woodland
Very rare. S. England (Oxford), C. Wales (Montgomery), Scotland (E. Ross).
Not refound recently in England (1980) or Wales (1979), but was recorded from a lichen rich old growth pasture woodland in eastern Scotland as recently as 2016. A very rare and threatened species.
Britain: Critically Endangered
Cannon, P., Prieto, M., Coppins, B., Sanderson, N., Scheidegger, C. & Simkin, J. (2021). Caliciales: Caliciaceae, including the genera Acolium, Amandinea, Buellia Calicium Diploicia, Diplotomma, Endohyalina, Monerolechia, Orcularia, Pseudothelomma, Rinodina and Tetramelas. Revisions of British and Irish Lichens 15: 1-35.
Text by Neil A Sanderson, based Cannon et al (2021)