Vegetative hyphae indistinct, surface mycelium absent.
Anamorph: not known.
Teleomorph: ascomata perithecia, (60–) 90–130 (–200) µm diam., subglobose, black, smooth, the ostiole 15–30 µm diam., almost always immersed, rarely slightly protruding in the ostiolar area, scattered and dispersed. Peridium 30–40 µm thick, dark bluish green above, often with a grey shade, hyaline below, composed of epidermoid to angular cells 3–10 µm diam., K−. Hymenial gel I−, K/I−. Interascal tissue of abundant narrow pseudoparaphyses 1·5–2·0 µm diam., septate with individual cells 6–15 µm long, rather frequently branched and anastomosed, not swollen at the apices. Asci (41–) 53–69 (–80) × (10–) 11–15(–18) µm, ± cylindrical, short-stalked to almost sessile, usually moderately thickened in the lower part, thick-walled and fissitunicate, often with a small ocular chamber, not staining in iodine, (4–) 8-spored. Ascospores arranged obliquely uniseriately or biseriately, (12·5–) 16·5–21·0 (–27·5) × (4–) 4·5–5·5 (–8) µm, l/b = (2·5–) 3·2–4·2 (–5·4), narrowly soleiform with an attenuated lower part, rarely almost ellipsoidal, the upper or both ends often acute, with (1–) 3 (–4) septa, not or slightly constricted at the septa (markedly so only when overmature), hyaline, smooth- walled, with a gelatinous sheath 1·0–1·5 µm thick.
Not assessed. The species is only known in GB&I from a single collection.
Distinguished from other species of Cercidospora associated with Thamnolia by the blueish green upper part of the peridium, the well-developed interascal tissue and the usually 3-septate ascospores with a gelatinous sheath.
On thalli of Thamnolia vermicularis, apparently a biotrophic parasite.
In GB&I, only known from a single site in VC92 S Aberdeenshire.