Lecanora rupicola (L.) Zahlbr. s.l.
Thallus crustose, highly variable, usually forming determinate patches or mosaics, to 10 cm diam., surface cracked, rimose to uneven, greyish, whitish, (sometimes pink see: Lecanora rupicola forme rose) margin thin, prothallus indistinct becoming black at the junction between several conspecific colonies, suggesting an aerial photograph of river meanders. Apothecia more or less immersed in the thallus at least at first, 1-2 mm diam., discs slightly concave becoming slightly convex, pruinose, pale brown-ochraceous, grey-pink, fawn, exciple whitish or paler, entire to crenulate. Well-fertile specimen are rather scarce and often apothecia are incompletely developed, and frequently parasitism due to Arthonia varians is prevalent if not the rule though other parasite species seem to coexist. Ascospores simple, ellipsoid, 9-15 x x 5.5-7 µm. Photobiont: Trebouxia. C-, K+ yellow, Pd-; apothecia discs C+ yellow (form-specific trait), K+ yellow (see infra the other reactions in this group). Common on well exposed siliceous rocks in the xeric supralittoral zone where it may form larges colonies and mosaics. Also frequent in the aerohaline zone and less frequently inland.
N.B. So many forms and morphotypes are found that it seems preferable here to consider a Lecanora rupicola group (or aggregate). If we add modifications due to the Arthonia varians parasite, and the variegated photobionts living in this lichen, that can influence its macroscopic appearance, it is rather difficult to give a precise and completely relevant description of this species in order to identifiy it in the field. According to some authors, the chemical spot tests are definitely required to that end, despite they can be disconcerting (can vary from a thallus to another, and even on the same one), and authors do not necessarily agree on their significance, because they aren't any clear and reliable correlation between the different characteristics (macroscopic, microscopic, chemical, ecological). The following pictures show some of these forms and the different aspects found notably on sligtly acid rocks. On an indicative basis is proposed herein below a classification approach principally based on chemical characteristics:
Lecanora rupicola (L.) Zahlbr. subsp. rupicola morpho. efflorens Leuckert & Poelt. Thallus : K+ yellow ; apothecia disc : C+ yellow. Presence of blue soredia. Mountains.
Lecanora rupicola (L.) Zahlbr. subsp. rupicola morpho. rupicola Thallus : K+ yellow ; apothecia disc : C+ yellow. Apothecia cream with ochracea almost sessile. Would be the most common.
Lecanora rupicola subsp. sulphurata (Ach.) Leuckert & Poelt. Yellowish thallus : K+ yellow ; apothecia disc C- but KC+ orange.
Lecanora rupicola subsp. suplanata (Nyl.) Leuchert & Poelt. Whitish thallus : K+ yellow ; apothecia disc : C- but KC+ orange. Rather uncommon.