It is the sorediated form of Syncesia myrticola which until a recent study has been confused with certain forms of Enterographa and in particular Enterographa crassa and also under the inappropriate name of Enterographa sorediata. Thallus thin, continuous, rimose to striated, greyish, covered with farinose soralia, whitish to pale grey, rounded, 0.5 mm in diameter, scattered but sometimes in a line along the fissures bordering the areoles or then confluent and forming large zones covered with refracting crystals. Very rare pycnidia. No apothecia or aborted. Medulla and soralia: C-, K-, KC-, P+ reddish, rusty red (sometimes weak and fleeting). Form occurring on the dry face sheltered from the rain of oaks (Quercus) in particular, very rarely on dead wood or worked wood; often with Dendrographa decolorans which is distinguished by its P- reaction ; also with Enterographa crassa and the question then arises as to whether this species is parasitic or whether it only exchanges its photobiont..
N.B. According to our observations, the sorediated form can be found at the same time as the form with apothecia, as is the case here in certain photographs.
Damien ERTZ, Brian COPPINS, Nell A. SANDERSON. The Britih endemic Enterographa sorediata is the widespread Syncesia myrticola (Roccellaceae, Arthoniales). The Lichenologist 50 (2): 153-160 (2018).
