Anamorph: not known.
Teleomorph: ascomata perithecia, almost completely immersed in the host thallus, the upper and lateral parts surrounded by a thick, very irregular involucrellum to ca 500 µm diam. with strongly melanized occluded cells, visible from the surface as a ± circular black patch 250-350 µm diam., irregularly roughened and sometimes appearing strongly cruciate, the ostiole not clearly distinguishable from the surface. Ascomata 350-420 µm diam., ± globose but also very irregular in section, the peridium composed of many layers of rather thick-walled mid brown flattened cells 6-11 µm diam. and 3-4 µm thick. Interascal tissue absent, the ostiole lined with recurved hyaline periphyses to ca 40 µm in length. Asci 75-95 x 18-22 µm, cylindric-ellipsoidal, ± sessile, the apex rounded, thick-walled and sometimes with a broad ocular chamber but without distinct wall layers, probably with rostrate dehiscence, mostly containing ca 64 spores. Ascospores (6-) 7.5-8.5 x (4-) 4.5-5.5 µm, broadly ellipsoidal, with a single median non-constricted septum, dark brown, fairly thick-walled, smooth, without a perispore or gelatinous sheath/appendages.
Not formally assessed, but rarely reported (indicated as Nationally Rare by Woods & Coppins 2012). The circumscription and host range of this species needs further examination.
Similar to Muellerella pygmaea but with slightly broader, smooth ascospores.
A biotrophic parasite on the thallus of Ophioparma ventosa, apparently not causing any degradation. Reports of the species on Protoparmelia badia and Rhizocarpon species need further examination.
Five records from northern and central Scotland, and a single report from Northern Ireland. BLS map here.