Arthonia incarnata Kullh. ex Almq.

K. Svenska Vetensk-Akad. Handl., n. f. 17, 6: 18, 1880
Description: Thallus crustose, endosubstratic, inapparent or visible as a whitish to pale olive-grey discolouration of bark, often delimited by a thin, dark prothalline line. Apothecia irregularly rounded to short-elliptical, adnate, slightly to strongly convex, pale brown to brownish orange, 0.2-1.2 mm across, without a proper margin. Epithecium faintly orange-brown, 5-10 μm high, K-; hymenium colourless to pale orange brown, weakly inspersed with oil-droplets, 45-75 μm high; paraphysoids richly branched and anastomosing, embedded in a dense gelatinous matrix, not markedly swollen at tips; hypothecium colourless to pale orange-brown, 20-65 μm high. Asci 8-spored, subglobose, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type, 40-50 x 14-20 μm. Ascospores (1-)2(-3)-septate, hyaline, sole-shaped with a distinctly enlarged upper cell, (11-)12-15(-18) x (4-)4.5–6(-7) μm, without epispore. Photobiont trentepohlioid. Spot tests: thallus K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a widespread, but very rare specie of acid to subneutral bark, confined to forests with a long ecological continuity, known from several localities in Northern and Central Europe. To be looked for in Italy.
Growth form: Crustose
Substrata: bark
Photobiont: Trentepohlia
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)

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Predictive model

Redinger, K. (1938) Arthoniaceae, Graphidaceae . In Kryptogamen-Flora von Deutschland, Österreich und der Schweiz. Band 9, 2 Abt., Part 1 (G. L. Rabenhorst, ed.): 181–404. Leipzig: Borntraeger