Protoparmelia atriseda (Fr.) R. Sant. & J. V. Wirth

   Thallus crustose, more or less prominent or globose, 1-4 cm diam., composed of small mounds of rounded or hemispherical verrucose areoles separated by a network of small crevices, bright, brown-reddish, brown-yellowish, brownish, brown-orangy, showing a thick and blackish prothallus. Apothecia usually numerous, at first immersed in the areoles, then slightly sessile, disc bright, brown to dark brown, exciple thin, concolourous to the thallus or paler. Ascus utrifom bearing 8 ascospores. Ascospores colourless, oblong, apices slightly rounded, 8-15 x 5-7 µm according to literature, 10-14 (16) x (4) 5-7 (8) µm according to our measurements. Photobiont: trebouxioid. C-, K+ yellow > orange, KC-, Pd+ yellow to orange, UV-. Parasite, at least at the beginning, of yellow Rhizocarpons and notably Rhizocarpon geographicum and Rhizocarpon lecanorinum thriving on acidic siliceous rocks.