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. 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.