Muellerella pygmaea  

Anamorph: not known.
Teleomorph: ascomata perithecia, (150-) 175-250 (-350) µm diam. and 130-250 µm tall, almost completely superficial on the host thallus, subglobose, ostiolate, the ostiole sometimes sunken, black, glabrous. Involucrellum not clearly differentiated, the ascomatal wall thick and robust, very strongly melanized with the cell walls mostly occluded, composed of many layers of rather thick-walled 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 80-100 x 22-27 µm, cylindric-ellipsoidal to saccate, ± 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 (7.5-) 8-10 (-13.5) x (3.5-) 4-5 (-6) µm, broadly ellipsoidal, with a single median non-constricted septum, dark brown, fairly thick-walled, smooth to finely verrucose, without a perispore or gelatinous sheath/appendages.