TYPE. [UNITED STATES. “CAROLINA”]. “In America septentrionali ad cortices laeves” (Nylander 1863), E. Tuckerman 267 (H H-NYL 5470).
Description. Lichenized fungus.
Thallus crustose, thin, not continuous, smooth, pale to greenish gray or brownish gray, 40-100 μm thick; vegetative diaspores absent; prothallus thin, black. Photobiont trentepohliod alga, cells globose to ellipsoid, 6-15 μm diam., in scattered clusters or short chains. Ascomata arthonioid apothecia (lacking exciple), immersed to adnate, roundish to slightly irregular, 0.5-0.7 mm diam., abundant, scattered or in groups of 2-3; disk flat, brown-black to black. Epithecium dark red-brown, 12-20 thick; hymenium hyaline to dark red-brown, 10-50 μm high; paraphyses indistinct; hypothecium dark red-brown. Asci 40−60 × 28−45 μm, 8-spored; ascospores hyaline becoming brownish at maturity, oblong-ellipsoid, submuriform to muriform, often curved, 22-35 x 8-12 μm. Pycnidia not seen.
Chemistry. Thallus section I+ red, K/I+ blue (hemiamyloid). Hymenium K+ olive, I+ orange-red, K/I+ blue. No secondary compounds detected by TLC.
Substrate and Habitat. Corticolous on trees in forests.
Distribution. Australasia (Australia, Tasmania, New Zealand), eastern North America (United States); in North Carolina found along the coast.
Fink, B. (1935) The Lichen Flora of the United States. University of Michigan Press, Ann Arbor (description as Arthothelium interveniens).
Kantvilas, G. (2021) A synopsis of the genus Arthothelium (Arthoniales) in Tasmania. The Lichenologist53: 415–431 (description as Arthothelium interveniens).
Nylander, W. (1863) Prodromus Florae Novo-Granatensis ou enumeration des plantes de la Nouvelle-Grenade. Lichenes. Annales des Sciences Naturelles Botanique20: 228-279 (original description).