Lecanographa atlantica Ertz & van den Boom
Lecanographa dialeuca auct. brit. non (Cromb.) Egea & Torrente
Thallus crustose, rather thick, smooth, uneven when growing in rock fissures, minutely farinose or slightly rugose, more or less cracked and areolate, white, whitish, white-pink, dark brown prothallus. Apothecia rather large, potentially occupying totally the areoles, completely immersed and very little or not protruding even when mature, highly variable in shape: rounded, elliptical to elongate or wavy or shortly lirelliform, blackish, covered with a dense whitish pruine when young, exciple absent. Ascospores fusiform, straight or slightly curved, 6-7 (8)-septate, 21-29 x 3.5-5.5 µm. Conidia straight, 5-7 x 1 µm. Photobiont: Trentepohlia. Thallus: C-, K- or rarely K+ pale yellow, Pd- or rarely P + yellow-orange (beginning of parasitism by Syncesia myrticola ?). Rare, thermophile species belonging to the Sclerophytetum circumscriptae, grows below siliceous sheltered rocks facing South. In the field, this species can be distinguished by its negative chemical reactions. N.B. Not to be confused with Arthonia atlantica which is K+ yellow and with different ascospores, and with some forms of Syncesia myrticola that are Pd+ yellow-orange.
N.B. Recently separated species of Lecanographa dialeuca which differs in its narrower lirelliform apothecia with a black non-pruinose margin and a different chemical composition.
N.B. Species very frequently parasitized by Syncesia myrticola which can make the determination very difficult.