Buellia leptoclinoides (Nyl.) J. Steiner
Thallus crustose up to 5 cm in diameter, rimose, areolate, pale yellowish-grey, greyish, with a black prothallus (especially in contact with another thallus). Sessile apothecia more or less numerous, 0.5-1 mm in diameter, disc flat to slightly convex, brown-black, black. Utriform asci, octosporous, 60-70 x 18-25 µm. Spores brown, elliptical, sometimes a little curved, very slightly warty (according to the literature!), walls sometimes thinned at the tops 1-(3) septate, 15-23 x 7-11 µm according to the literature, 17-21 x 10 -11 µm according to our measurements. Pycnidia frequent, black. Photobiont: Clorococcales. C-, K+ yellow, P+ yellow,. Medulla I-. On siliceous rocks in dry places of the xeric supralittoral zone. Easy to confuse with other species of crustose lichens, but with different colored chemical reactions
N.B. Sometimes in the field similar to Buellia saxorum but the latter species is C+ pink-orange and has smaller spores.