Buellia disciformis (Fr.) Mudd

    Thallus crustose, 2-4 cm maximum length., thin, smooth to satin-smooth, rimose-cracked and somewhat warted, whitish, pale dull white-grey to yellow-grey, often delimited by a black prothallus (mostly in contact with other thalli). Apothecia superficial and sligthly sessile, rounded, 0.5-1 mm diam.; disc flat to slightly convex, black, true exciple usually persistent, concolourous but sometimes with white pruine. Ascospores brown, broadly ellipsoid, sharp apices, 1(-3) septate, 15-25 x 7-10 µm. Photobiont : Chlorococcales. Thallus: C-, K+ yellow, Pd+/- yellow, medullae : I-. Uncommon in our prospection area, on smooth bark deciduous trees.*