Mycomicrothelia wallrothii (Hepp) D. Hawskw.

Syn.: Didymosphaeria wallrothii (Hepp) Sacc. & Trotter, Massariopsis wallrothii (Hepp) Rehm, Microthelia betulina J. Lahm, Microthelia wallrothii (Hepp) Grummann, Pyrenula wallrothii Hepp
Non- or doubtfully lichenised.
Substrate: bark
Altitudinal distribution: montane belt (potential vegetation: deciduous forests dominated by Fagus sylvatica and closed coniferous forests with Picea abies)
Note: an apparently non-lichenised species with ascomata (to c. 0.25 mm in diam.) immersed in the periderm of the host tree, with a well-developed ascomatal fringe, a dimidiate, dark brown involucrellum consisting of host cells and intermingled hyphae (the wall of intricate hyphae), numerous, anastomosing and persistent interascal filaments, 8-spored, fissitunicate asci, dark brown, 1-septate ascospores (16-18 × 7-8 µm) with more or less equal cells and a thin, indistinctly verruculose perispore, and conidiomata inbetween the ascomata containing 1-distoseptate, ellipsoid conidia; on bark of Betula, rarely Populus; widespread in the Holarctic region, in the study area only recorded from the Eastern Alps (Austria).
Austria: Salzburg;