Pectenia atlantica (Degel.) P. M. Jørg., L. Lindblom, Wedin & S. Ekman  morpho atlantica ss. str.

= Degelia atlantica (Degel.) M. Jørg. & P. James

   Thallus foliose rosette-shaped, up to 5-10 cm diam., made of fan-shaped or "knife-painter" lobes tightly appressed on substrate, lobes often concave, wrinkled and wrinkled longitudinally and without network, lead gray, dirty bluish gray, pale brownish gray with upwardly curved ends looking finely ciliate, light brown, milk-coffee, paler margin sometimes uncovering the lower fibrous whitish to blue-dark prothallus; upper surface gradually covered from the center by nodulose or partially coralloid isidia that become confluent and may cover the whole surface of the thallus, pale grey-brown, dull grey-blueish. Apothecia rare and scattered, immersed (not sessile), but sometimes locally crowded and then distorted, 0.5-1 mm diam., disc flat, brown-reddish, reddish to blackish when dry, margin clear, concolourous or paler. Ascus utriform, 60-70 x 20-25 µm according to our measurements. Ascospores ellipsoid, colourless, (14) 17-20 (23) x 7-9 (12). Photobiont: Nostoc. Chemical spot tests negative. Rare oceanic and Macaronesian species, growing on mossy barks of old trees in old woodlands, possibly on mossy rocks. The presence in France of this species is only confirmed for a single harvest because it is very close to Pectenia plumbea and especially to certain of its forms bearing isidioid granules with which it has been confused (in particular by British authors), but Pectenia plumbea has brighter colours with less beige, a light blue prothallus and a very fertile non isidiated thallus. Intermediate specimens may exist : see Degelia plumbea forme à gros granules isidioïdes and Degelia plumbea forme à petits granules isidioïdes. 

_ See also Pannaria conoplea that grows in the same woodlands (and sometimes on the same tree) displaying incised lobes at margins, lobules instead of isidia and much more blueish colours.

_ See also Pannaria mediterranea more grey-blueish and with thallus totally covered with grey soralia, grey-blue or grey-olivaceous and most of time sterile; and Pannaria rubiginosa with lecanorine apothecia and upper face of the thallus without any thin network, and is Pd+ orange.