Anamorph: not known.
Teleomorph: ascomata apothecial but initially appearing perithecial, 100-150 µm diam., immersed in irregular bullate deformations of the host lichen, not erumpent and the opening slightly depressed, numerous, arising singly but often crowded together, not stromatic, subglobose to obpyrlform, subhyaline to pale reddish or olivaceous, the opening 25-50 µm diam., sometimes becoming more expanded with age. Peridium composed of 3-6 layers of interwoven hyphae, subhyaline to pale reddish, orange-brown or olivaceous especially near the ostiole, mainly 7-10 µm thick but sometimes to 15 µm thick near the ostiole, hyphae of the wall mainly 2-3 µm diam. with narrow lumina and thick hyaline walls. Interascal tissue composed of paraphyses 1.5-2.5 µm diam., arising from the base of the ascomatal cavity, numerous, persistent, filiform, sparsely septate, unbranched, variable in length, some extending into the ostiolar region, tips not markedly differentiated and with no tendency to form a distinct epithecium. Asci (50-) 65-90 x 5-7 µm, arising in a fascicle, cylindrical to elongate-clavate, unitunicate, the wall ± equal in thickness when mature but apex slightly thickened in young asci and including an indistinct 'chitinous' area, not reacting with iodine, 8-spored. Ascospores overlapping and biseriate to almost uniseriate, 8-10 (-11) x 3-5 µm, ellipsoidal to fusiform with obtuse ends, aseptate, hyaline, 0-2 guttulate, smooth- and thin-walled, without an epispore, gelatinous sheath or appendages.
Assessed by Woods & Coppins as Data Deficient and feared extinct, until rediscovered in 2017 at one of the original sites that was reported in the nineteenth century. Further survey work would be desirable.
A distinctive gall-forming fungus. distinguished from the non-GB Cercidospora thamnogalloides by its aseptate ascospores and its broadly opening fruit bodies.
Parasitic on thalli of Thamnolia vermicularis, forming distinctive galls but not otherwise apparently causing damage.
In GB&I, modern records are only from one mountain in VC92 S Aberdeenshire; it was formerly known from Ben Lawers and Cadair Idris. BLS map here.