Hypotrachyna britannica (D. Hawksw. & P. James) Barbero

    Thallus foliose, moderately adnate to appressed, to 8 cm across, lobes erect, more or less imbricate , 1-4 mm wide, apices rounded, more or less irregularly incised, upturned, seldom ciliate, upper surface smooth, cortex delicate possibly breaking up into squamules, pale grey, pale blue-grey, pale  ash-grey, with submarginal pustulose distinct sorelia, becoming coarsely sorediate, dark blue, indigo-blue, dark and almost blackish when dry, lower surface matt, more or less veined or caniculate, dark brown to black, moderately rhizinate, rhizines short, dichotomously branched, black or brown-black. Apothecia unknown. Photobiont: trebouxioid. Cortex : K+ yellow, Medulla: C+ pale red, K-, KC+ red, Pd-. Oceanic and coastal trends, on siliceous rocks in well-lit sites of the aerohaline zone, sometimes on the ground or on old Calluna stems and branches, rarely on hulls of shipwrecks in marine cemeteries, see: Hypotrachyna britannica forme sur substrat artificiel. 

 _ Not to be confused with Hypotrachyna revoluta (Flörke) Hale that is not restricted to coastal areas, without indigo-blue soralia but instead farinose and greenish soredia. Not to be confused either wit saxicolous forms of Hypotrachyna afrorevoluta (Krog & Swinscow) Krog & Swinscow (sometimes considered as belonging to the same species: additional molecular biology analyses would be required here) of which the soredia usually are paler and above all the lower surface is glossy with numerous long and unbranched rhizines.