Fuscidea lygaea (Ach.) V. Wirth & Vezda
Thallus crustose, round shaped, rather thin, up to 2-5 cm diam., areolate to rimose-cracked, greyish, pale to dark grey-brown or dark brown, often with a purplish or violet tinge, prothallus usually present, thin, blackish, bordering thallus. Apothecia 0.2-0.5 mm diam., possibly scattered but usually clustered towards the center, emergent to adpressed, sessile, disc flat then markedly convex, blackish, margin concolourous, thin, soon excluded. Ascii 8-spored, 45-55 x 15-20 µm according to our measures. Ascospores colourless turning brownish when mature, very broadly ellipsoid to subspherical, 6-10 x 5-7 µm, (6-11 x 5-8 µm according to our measures). Photobiont: trebouxioid. Chemical spot tests negative. This species has uplands to montane trends but may also be found on vertical walls of humid siliceous rocks in cliff surfaces (sometimes with Ionaspis ceracea in the Finistère in Brittany and with Ephebe lanata in Cap Finisterre in Spain). Easily confused with Fuscidea cyathoides that is a much more common species and that grows in dryers and well-lit locations, K+ dull yellow, Pd+ reddish, and with kidney-shaped ascospores. Not to be confused with some species of Rhizocarpon, more areolate and with apothecia exciple permanent and above all, muriform ascospores.