Myriolecis semipallida (H. Magn.) Sliwa, Zhao Xin & Lumbsch
Lecanora flotoviana auct. non Spreng.
Lecanora xanthostoma C. Roux ex Fröberg
Lecanora semipallida H. Magn.
Thallus crustose, thin and evanescent, more or less endolithic, margin effuse, dark grey, dark grey-yellowish, blackish often with bluish spots. Apothecia sometimes isolated to dispersed or most often in small clusters, more or less crowded, 0.5-1.5 mm diam., sessile to constricted, disc flat, yellowish, pale yellow-orange, pale grey-brownish, pale brownish, sometimes with blue spots or slightly powdery, exciple determinate, thick, flexuous to crenulate, white and strongly contrasting in colour with the thallus, farinose. Granules, dissolving in K, within epithecium. Ascospores hyaline, ellipsoid, simple, 8-13 x 5-7.5 µm. Photobiont: Trebouxia. Presence of vinetorin. Thallus: C-, K-, Pd-, UV-; discs: C+ yellow-orange, K+ yellow-orange, Pd-, UV+ orange; exciple: C+/- yellow, K+ yellow, KC+ yellow, Pd-, UV+ yellow-orange. Not especially maritime, on calcareous or slightly calcareous rocks, on species (or close to) dependent on these substrata: Aspicilia sp., Caloplaca sp. Verrucaria sp.. This species belongs to the Myriolecis (Lecanora) dispersa sensu lat. group. Not to be confused with other very close species: Myriolecis (Lecanora) dispersa of which the thallus is whitish, epithecium devoid of crystals and with negative chemical reactions; Myriolecis (Lecanora) invadens H. Magn. of which the apothecia disc is powdery, dark brown or lead-grey to blackish, but this taxon may be conspecific. N.B. Some authors rank Lecanora xanthostoma, of which exciple is yellow and UV+bright yellow-orange, as a different form.
Extremely variable species and very variously interpreted by the authors! See a thin cream-yellowish margin form under: Myriolecis (Lecanora) semipallida forma