Lecanora cenisia Ach. ss. auct. brit. Cf.

    Thallus crustose, areolate and slightly verrucose, whitish, greyish, dull pale greyish, prothallus whitish, bluish, dark bluish, sometimes pink in places exposed to seaspray. Apothecia usually numerous, 1-2 mm diam., markedly sessile at the end, disc red, brown-reddish, brownish, greyish, blackish, epithecium brownish, exciple persistent, entire to crenulate, wavy with large refringent crystals in the medulla. Ascospores simple, colourless, ellipsoid, 9-15 x 6-8 µm according to literature ; 13-18 x 5-7 µm according to our measurements. Photobiont: Trebouxia. Thallus: C-, K+ yellow or K+ yellow > red, Pd+ yellow to red-orange. Rare, on more or less vertical walls of rough siliceous rocks near the seashore. N.B. Interpretations of this species are diverse and confusing. For French authors, this taxon would be montane. For British authors, it would be also coastal and we follow this latter interpretation. In addition, in our prospection area (to our knowledge) 3 different species sharing the same habitat and the same chemical reactions may be found: 1) the present taxon, 2) Lecanora gangaleoides of which epithecium is greenish and thallus more verrucose, K+ yellow, disc blackish with a large whitish exciple, 3) Lecanora praepostera with a thallus dull whitish and apothecia markedly sessile, blackish and often restricted to a small empty cupule.

N.B. It seems that this taxon is interpreted as Lecanora praepostera s.l. by the French authors.