Xanthoparmelia tinctina (Maheu & A. Gillet) Hale

    Thallus foliose, most often rosette-shaped, lobes 2-6 mm wide, apices wavy, upper surface grey-yellowish, grey-whitish when dry, grey-greenish with pale bronze tinge when moist, covered with isidia, most of them swollen or with globose tips, possibly covering a major part of the thallus, lower surface blackish, with a few simple black rhizines. Apothecia scarce, lecanorine, sessile, 0.5-1 cm diam., disc concave to flat, brown-reddish, exciple wavy, markedly prominent, concolourous. Ascospores simple, colourless, broadly ellipsoid, 6-10 x 4-5 µm. Photobionte: trebouxioid. Cortex: K-; medulla: C-, K+ yellow > red or brown-red, KC+ red, Pd+ orange. Rare, on the highly exposed siliceous rocks of the foreshore. This species is very similar to Xanthoparmelia conspersa  and is sometimes difficult to distinguish to the naked eyes, but differs by its isidia covering, swollen and globose (though this characteristic is not fully reliable) and only its chemical reactions, i.e. medulla K+ red, allow a reliable differentiation between these two species. N.B. The distribution of this species seems to be limited to Anglo-Norman islands, South of England, Ireland and the western coasts of Brittany also in the Atlantic Islands; but there is a much more frequent taxon on the shores of the Mediterranean, see: Xanthoparmelia tinctina taxon de Méditerranée.