Arthopyrenia platypyrenia (Nyl.) Arnold

Non-lichenized corticolous fungus.

      Thallus (in the strict sense) absent, this species not being lichenized, but sometimes visible as a discolored zone. Perithecia developing under an involucrellum that is sometimes lateral and offset, circular to ovoid, slightly protruding with a flattened apex, ostiole reduced to a slit, black to blackish. Asci clavate, 8-spored, 105-125 x 18-25 µm according to literature, 90-110 x 18-20 µm according to our measurements. Spores hyaline, graying in old age, 3-4 (6) septa, constricted to septa, with 1 µm gelatinous layer, 23-27 x 8-11 µm according to literature, 25-28 x 9-10 according to our measurements . C-, K-, KC-, P-. Fairly common species typically growing on the twigs of ivy (Hedera helix) growing on the trunks of trees, especially in the woodlands by the sea but sometimes further in the humid forests.

N.B. A microscopic check is often necessary to identify this species with certainty, because there are many similar species in this kind of habitat.