Enterographa crassa (DC.) Fée

    Thallus crustose, rather thick, 2-4 cm across max., often forming wide-spreading complex mosaics, thalli delimited by conspicuous black persistent prothalli, surface smooth or faintly rimose-cracked, forming a minute network-like, colour highly variable : pale grey, pale brown to grey-brown,  brown-olive, brown-green. Apothecia usually very numerous, sometimes clustered at margin close to prothallus, 0.1-0.3 x 0.1 mm, deeply immersed, brown-black, punctiform or narrowly ellipsoid, in small clusters or dotted or thread-like lines or cuneiform writings on thalli. Ascii cylindrical 110-130 x 10-14 µm according to our measurements. Ascospores colourless, narrowly ellipsoid, 5-7-septate, 28-40 x 4-6 µm accroding to literature ; 28-38 x 4-6 µm according to our measurements. Pycnidia frequent, punctiform. Photobiont : Trentepohlia. Thallus : C-, K-, KC-, Pd-, UV-, K/UV+ blue. Atlantic trends and therefore abundant in our prospection area, on shaded bases and trunks of deciduous trees (notably Quercus), sometimes in large colonies, rarely on very shaded, humid, siliceous rocks.

N.B. This species is highly variable and probably includes several taxa. Usefully compared to Enterographa elaborata ss. auct. brit. with larger ascospores, apothecia long and sinuous, and paler thallus; and to Enterographa hutchinsiae ss. larg. with brown-olive thallus, cracks yellow edged, without black prothallus, apothecia lirelliform, short, broad and irregular.

We can isolate from this very variable species some particular forms:

_ Enterographa crassa forme sur Ulmus with small apothecia.

_ Enterographa crassa form on Ilex, with tiny apothecia visible only with a magnifying glass and whitish hypothalle.