Synonyms: Arthonia lurida auct. ital. p.p. non Ach.; Coniangium luridum auct. non (Ach.) Fr.; Coniangium vinosum (Leight.) A. Massal.
Distribution: N - Frl, Ven (Nascimbene & al. 2005b, 2006c, 2013b, Thor & Nascimbene 2007), TAA (Thor & Nascimbene 2007, Nascimbene & al. 2007b, Nimis & al. 2015), Emil (Tretiach & al. 2008, Fariselli & al. 2020). C - Tosc, Laz (Herb. Ravera 2887), Abr (Nascimbene & al. 2021), Sar (Cossu 2013). S - Cal (Puntillo 1996).
Description: Thallus crustose, thin, immersed or thinly powdery to granular, whitish to ochre-coloured, often stained yellow-orange, especially around the apothecia. Apothecia arthonioid, irregularly rounded in outline, 0,3-0.8(-1) mm across, 85-140 μm tall, convex, orange-red-brown to brown-black, red-brown when wet, epruinose. Epithecium indistinct; hymenium yellow-orange, (30-)40-50(-60) µm high, K+ purple-violet (the pigments dissolving), I+ red-brown; paraphysoids 0.5-1.5 µm thick, usually not much swollen at apex; hypothecium dark red-brown in upper part, up to 30 µm high, K+ purple-violet. Asci 8-spored, broadly ovoid, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type. Ascospores 1-septate, with slightly unequal cells, ovoid-ellipsoid to slightly clavate, colourless (but old ascospores brown and warted), (9-)11-15(-17) x 4-6(-7) µm. Pycnidia frequent, the wall red-brown, K+ purple. Conidia bacilliform, straight or slightly curved, 4-6 x c. 1 µm. Photobiont trentepohlioid. Spot tests: thallus K+ purple on pigmented spots, C-, KC-, P-, UV-. Chemistry: unidentified anthraquinones in thallus and apothecia.
Note: a mild-temperate lichen found near the base of old trees, mostly on rough bark, especially of oaks, more rarely on lignum, in very humid and closed-canopied deciduous forests. Young or depauperated forms may be confused with A. didyma. The species is included in the Italian red list of epiphytic lichens as “Near-threatened” (Nascimbene & al. 2013c).
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)