Porina pseudoapplanata Lücking & Cáceres sp.nov. is characterized by its foliicolous growth habit, a thin, nitidous thallus without crystals, applanate, yellowish red perithecia narrowly bacillar, 7-septate ascospores, and the presence of previously unrecognized isidi belonging to the Phyllophiale-type, here formally described as P. viridis Lücking & Cáceres sp.nov. The interpretation of Phyllophiale representing isidia of Porina species is discussed. Porina pseudoapplanata is similar to species in the P. rufula group, i.e. P. monocarpa (Kremp.) F. Schill., P. cupreola (Müll. Arg.) F. Schill., P. planiuscula Vêzda and, in particular, P. applanata Vain. However, it seems most closely related to P. mirabilis Lücking & Vězda in the P. epiphylla group, from which it differs by the complete absence of crystals in the thallus and perithecia. This gives a further insight into systematic relationships within the Trichotheliaceae. Keys are presented to distinguish P. pseudoapplanata from similar and related species, as well as to the known species of Phyllophiale.