Tephromela atra (Huds.) Hafellner var. atra
Thallus crustose, to 15 cm across, usually rather thick, more or less irregular and cracked, areolate, whitish to pale dull white-greyish, margin thin, prothallus black. Apothecia developing on a regular pattern from the center, sessile, 1-3 mm diam., disc flat, black, exciple white, thick, irregular, contorted to wavy, more or less crenulate; in section, the hymenium is purple, sometimes directly visible in old empty apothecia. Ascospores simple, ellipsoid, 10-15 x 6-8 µm. Photobiont: Chlorococcoid. C-, K+ yellow, KC+ yellow, Pd-. Not especially maritime, and found everywhere on nutrient-rich acid rocks, but also rather common in the aerohaline zone where sometimes it contributes to the development of the 'white belt'. Near the seashore, this species is easily mistaken with Lecanora gangaleoides that is strongly maritime. The latter may be distinguished (sometimes difficultly) by its thallus greyish tinged-green and its margin, whitish, its apothecia with convex discs when mature and exciple regular, not contorted nor wavy, and above all its hymenium, brown-green in section.
Two varieties of this common species are described:
Tephromela atra var. calcarea that grows on calcareous rocks.
Tephromela atra var. torulosa that grows on smooth bark of deciduous trees notably Fagus.
N.B. This species has a very slow growth as shown by the two photographs of the same thallus taken almost 5 years apart.