Mycoporum antecellens (Nyl.) R. C. Harris

      Thallus quite variable depending on the substrate, crustose, thin, encrusted in the substrate, smooth, whitish, gray-whitish, greenish-gray, pale brownish. Perithecia buried in the thallus and not protruding, irregularly arranged on the thallus, often in small crevices of the thallus, hemispherical to ovoid, 0.2-0.3 mm in diameter, black. Pyriform asci, 60-70 x 18-22 µm according to the literature, 60-80 x 25-35 µm according to our measurements. Spores claved, hyaline then gray-brownish and very finely warty, most often 1-septate with a narrowing at the septum delimiting two cells of unequal size but sometimes with a 3-septate appearance by the formation of 2 secondary cells in the primary cells ( without shrinkage), 27-40 x 8-13 µm according to the literature, 25-35 x 7-10 µm according to our measurements. Black pycnidia often numerous. No color reactions to the usual reagents. Photobiont: absent, this species probably not being lichenised. Probably rare species of Graphidetum, coming towards the base of the trunks of trees with more or less smooth bark in old forests under oceanic influence.

See many species of Arthonia with which this species is distinguished with certainty only by its large spores.