Syncesia myrticola (Fée) Tehler

    Thallus wide-spreading, to 10 cm across, irregular, thick, nodulous or even cerebroid, madrepore-like, some nodules and foldings may reach 1 cm thick, fragile, felted-like, water-repellent, chalk concretion shaped, chalk or grey-white to pale grey, whitish tinged pink or brown-pink to beige-pink, dull pink-violet purple when old (N.B. Wounds often allow to see the yellow-orange photobiont). Fruiting bodies with characteristic shape: cubicles included in the thallus and initially appearing externally as cerebriform patches or well-worn ruminant molar shaped or madrepore-like on a white chalk-like thallus, then spreading as irregular discs, innate and little prominent, blackish, covered with a white long lasting  pruine, the thallus then turns to dull beige-grey. Asci club-shaped, weakly amyloid, 90-100 x 25-30 µm according to our measurements, containing 8 spores. Colorless fusiform spores with unequal (one tapering, one rounded), straight or slightly curved ends, (1)-(2)-3- septate, 35-44 x 4-5 µm according to the literature; 36-45 (50) x 4-5 (6) µm according to our measurements. Photobiont: Trentepohlia. Thallus : C-, K-, Pd+ red-orange (but sometimes difficult to interpret due to interference from the parasitized host). Mediterranean or Macaronesian coastal species usually growing on bark and rocks. In Brittany, our usual prospection area, this species seems to be restricted to vertical walls or overhangs protected from rain on rocks in highly exposed foreshore locations, frequently in association with Roccella fuciformis ou Roccella phycopsis of which the colour is rather similar and also with species belonging to the Sclerophytetum circumscriptae. Highly variable species, difficult to identify notably when mixed as parasite with other species.

N.B. The synonymy of this taxon is puzzling and it would require a complete revision. Specimen found in Brittany may well be parasites, in a similar way as 'Lecanographa grumulosa s.l.' and might be differently ranked (see the following example :  Syncesia myrticola parasite of Roccella phycopsis and Syncesia myrticola parasite d'Enterographa crassa.

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).