Pleurosticta acetabulum (Neck.) Elix & Lumbsch
Thallus foliose, rosette-shaped, 10-15 cm diam., composed of lobes, 0.5-1.5 cm wide, rather thick and resistant (rubber-like), margin rounded more or less ascending and contorted notably towards the edges, upper surface matt, green-greyish, olive-greeen when dry, green, bright and glossy when moist, with numerous black dots corresponding to pycnidia, mostly towards the lobe margins, lower surface pale brown with simple rhizines. Apothecia usually numerous, bowl-shaped, large, 0.5-2 cm diam., between markedly sessile and shortly stalked, disc concolourous to the thallus at first, then brown-red to brown-orange, exciple wavy and irregular or crenulate and whitish as below apothecia. Ascospores colourless, simple, ellipsoid, 14-17 x 7-9 µm. Photobiont: Trebouxioid. Cortex: C-, K+ yellow; medulla: C-, K+ red, KC-, Pd+ orange. Thermophilic, on bark of deciduous trees in well-lit habitats; reported to be common formerly but rare nowadays in our prospection although observed recently. N.B. Not to be confused with some fertile species belonging to the Melanelixia ou Melanohalea genera and notably with Melanelixia glabra, mediterranean thermophile species distributed in the South of France with smaller lobes and devoid of pycnidia towards the margin and with K-, C+ red medulla*.