Opegrapha niveoatra (Borrer) J. R. Laundon

    Thallus crustose, very thin, superficial, sometimes inconspicuous, more or less smooth, sometimes cracked, whitish, greyish, brown-greyish, brown-olivaceous. Apothecia lirelliform, small, 0.5-1 x 0.1-0.2 mm, little prominent, 0.05-0.1 mm height, simple, straight or curved, seldom forked, disc slit-shaped, opening gradually with maturation, rough, blackish. Ascus 80-90 x 12-15 µm according to our measurement. Ascospores quite elongated, acicular, 4-7-septate, 20-30 x 2,5-4 µm, and 25-30 x 3-4,5 µm, according to literature and our measurement respectively. Pycnidia always present, numerous, blackish, producing short and curved conidia (N.B. There are specimens with only pycnidii but linked to fertile specimens by intermediary ones). Chemical spot tests negative. Inconspicuous species, on alkaline or neutral bark of deciduous trees. See Opegrapha vulgata of which the apothecia are larger and the conidia larger, straight or sickle-shaped.*