Punctelia subrudecta (Nyl.) Krog

    Thallus foliose, rosette-forming, 5-8 cm diam., lobes tightly appressed to the substratum, 5-10 mm wide, upper surface grey-greenish, greyish, tinged green when moist, pseudocyphella punctiform, whitish, where arise, mainly from the center and from aged zones, numerous farinose soralia, soralia whitish to pale grey-greenish (notably laminal), lower surface dull whitish towards the center and pale brownish towards the margin (visible upper margin devoid of pruine sometimes is brownish), with simple rhizines (there is no consensus among authors about this specific trait and this is illustrated by our pictures that clearly demonstrate the diversity of coulours). Apothecia very rare, but see: Punctelia subrudecta forme fertile, sessile, urceolate at first then bowl-shaped, 3-5 mm diam., disc brown-red, thalline exciple markedly turned up with soralia, concolourous to the thallus. Ascospores simple, colourless, 15-18 x 8-11 µm, 14-18 x 7-10 µm  according to our measures. Photobiont: Trebouxioid. Cortex : K+ yellow ; medulla : C+ carmine, K-, KC+ red, Pd-, UV-. Rather rare, on trunks and main horizontal branches of trees, more seldom on rocks or walls, very rarely on artificial substrates: Punctelia subrudecta forme sur substrats artificiels.

   Not to be confused with Punctelia borreri characterized by C+ pink medulla and a blackish lower surface, paler at edges (secondary and variable trait), pseudocyphella bright whitish strongly contrasting with the thallus and less numerous soralia, and with Punctelia reddenda, more green-yellowish and with a C- medulla, and with Punctelia jeckeri of which the lobes are pruinose and brownish towards the margin and the soralia mostly terminal.

N.B. Intermediate specimen between Punctelia borreri and Punctelia subrudecta may be found.

In addition, not to be confused with some forms of Parmelia sulcata with medulla and soralia K+ red-orange and Pd+ orange.*