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Family: ArthoniaceaeGenus: Arthonia
Anamorph: not known.
Teleomorph: ascomata arthonioid apothecia, 80-180 µm diam., irregularly pulvinate, scattered or arregated and sometimes coalescing, brownish black, glossy. Epihymenium olivaceous, somewhat greener in KOH. Hymenium light brownish gray, sometimes almost hyaline below, ca 30 μm tall, I+ red, K/I+ blue. Interascal tissue of flexuous branched paraphyses with apical cells pigmented, 2.5‒5.5 μm diam. Subhymenium light to medium olive brown or brown. Asci 23‒27 × 15‒18 μm, broadly clavate to almost globose, very thick-walled, fissitunicate, 8-spored. Ascospores 10.5-13.5 x 3.5-4.5 µm, soleiform to clavate, (1-) 2-septate, the upper cell rounded and wider than the others, the lower cell becoming subdivided at a later stage, hyaline, smooth, with a gelatinous sheath ca 1 µm thick that often appears to degenerate at maturity of the spores.