Synonyms: Arthonia cytisi var. meridionalis Zahlbr.; Arthonia dispersa var. excipienda (Nyl.) H. Olivier; Arthonia hibernica Nyl.
Distribution: N - TAA (Nascimbene & al. 2007b), Lig (Brunialti & al. 2001). C - Tosc, Umb (Ravera 1999, Ravera & al. 2006), Abr (Caporale & al. 2016), Mol (Caporale & Ravera 2020). S - Camp (Garofalo & al. 2010), Bas (Potenza & al. 2010, 2014), Cal (CLU 16686), Si (Cataldo & Ravera 2013c).
Description: Thallus crustose, endosubstratic and usually poorly evident. Apothecia arthonioid, mostly lirelliform, up to 1.5 mm long and 0.3-0.5 mm wide, straight or curved, simple or rarely sparingly branched, with an initially slit-like, later somewhat expanded, brown, epruinose disc, and a slightly raised marginal zone. Proper exciple evident, containing remains of bark cells, 12-40 µm wide, dark brown, the pigment K+ green; epithecium pale brown to olive-brown; hymenium colourless, not inspersed with oil droplets, 50-80 µm high, I+ blue; paraphysoids 1-1.5 µm thick, without apical brown caps; hypothecium colourless. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type. Ascospores 1-septate, hyaline, ovoid, (14-)15-25 x 6-8(-10) µm. Photobiont absent, but thallus reported to be loosely associated with trentepohlioid and/or chlorococcoid algae. Spot tests: K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: on the smooth bark of deciduous trees and shrubs in riparian montane woodlands; probably overlooked, or confused with Naevia punctiformis. The species is included in the Italian red list of epiphytic lichens as “Vulnerable” (Nascimbene & al. 2013c).