Acrocordia gemmata (Ach.) Massal.

   Thallus crustose, thin, more or less smooth and cracked, white or pale grey, pale grey-green, hypothallus not visible. Perithecia hemispherical more or less immersed in thallus, 0.5-1 mm diam., blackish, one quarter to entirely immersed with an ostiole on top  often eccentric and sometimes papilla-like. Ascii narrowly cylindrical, apical dome with a broad ocular chamber surmounted by a hemispherical meniscus-like structure, 8-spored. Ascospores ellipsoid, 1-septate with a finely granular perispore, 18-30 x 8-12 µm according to literature, 20-27 x 9-12 µm  according to our measures.  Pycnidia rare and dispersed, 0.1-0.25 mm diam. Conidia 3-5 x 0.8-1 µm. Photobiont : Trentepohlia. Thallus : C-, K-, KC-, P-. Widespread and locally common species on rough bark decidous trees.

N.B. Possible confusion with Anisomeridium biforme (smaller perithecia and more numerous pycnidia with black hypothallus) and  Pyrenula macrospora (brown-green thallus delicately spotted).

N.B. There is a very similar species Acrocordia cavata, with smaller spores which is much rarer and localized.