Arthonia toensbergii, a new lichenicolous fungus on Mycoblastus affinis from the boreal rainforests in Norway

Abstract

Arthonia toensbergii is described from old-growth boreal rainforests in Norway. The new species parasitizes Mycoblastus affinis growing on branches and trunks of Picea abies. It can be recognised among related species by its combination of characters including the adnate, non-aggregated, matt, (brownish-)black ascomata not visibly breaking through the host thallus, 0.07–0.15 µm diam; medium olivish brown epi- and hypothecium without distinct apical caps on the tips of the paraphysoids; hyaline, slipper-shaped, 1-septate ascospores with slight constriction at the septum, 11–14 × 4–5.5 µm; hymenial gels I+ vinose, KI+ sky blue; and a KI+ blue ring in the tholus. Arthonia toensbergii is shown to belong to the Bryostigma-clade by RAxML and Bayesian analysis of mtSSU, nLSU, and RPB2 sequence data. The related species Arthonia parietinaria is reported as new to Norway.