Myriospora signyensis Purvis, Fdez-Brime, M. Westb. & Wedin is described from Signy Island, South Orkney Islands, Antarctica, where it occurs predominantly on quartz mica schist. This represents the first record of the genus for Antarctica. The distinctive interrupted photobiont arrangement places it within the genus Myriospora (formerly known as the ‘Acarospora’ smaragdula group, or Silobia). The new species is characterized by having large, distinctly elevated, sessile apothecia with a prominent margin and a thallus that is usually lobed at the margins and variously orange-red, rust-coloured or brown-pigmented. Molecular phylogenetic analyses inferred with strong support that M. signyensis is closely related to M. scabrida which is similar in having a lobed, imbricate thallus with large and frequently somewhat raised apothecia, but which differs in never being rusty red, by frequently having a larger number of apothecia per areole/squamule and by having a thick and distinctive thalline epinecral layer. Myriospora signyensis is otherwise most similar to M. dilatata but the thallus of M. dilatata is never imbricate-lobate and the ascomata of M. signyensis have larger and more distinctly raised and sessile apothecia. A worldwide key to the 10 species currently recognized in the genus is presented.

The new genus Silobia M. Westb. & Wedin is proposed for the Acarospora smaragdula group, which is taxonomically and nomenclaturally revised in Sweden. The proposed taxonomy results from our former molecular phylogeny, together with morphological and anatomical investigations and analysis of secondary metabolites. Seven species are recognized in Sweden in this paper: Silobia dilatata sp. nov., S. myochroa sp. nov., S. rhagadiza comb. nov., S. rufescens comb. nov., S. scabrida comb. nov., S. smaragdula comb. nov. and S. tangerina sp. nov. Acarospora alberti, A. amphibola, A. isortoquensis, A. murina and A. undata are recognized as synonyms of S. smaragdula, Acarospora verruciformis as a synonym of S. scabrida and A. scyphulifera as a synonym of S. rhagadiza. The following names are lectotypified: Acarospora amphibola, A. amphibola f. testacea, A. lesdainii, A. lesdainii var. subochracea, A. murina, A. scyphulifera f. subdiscreta, Endocarpon smaragdulum, Lecanora rhagadiza and Sagedia rufescens. Acarospora scyphulifera is neotypified. Acarospora fusca is excluded from the Swedish checklist as the specimen was found to belong to S. rufescens. A key to the species is presented.

Acarospora rosulata is revised and reported from North America and Mongolia. Acarospora bullata is not verified as occurring in South and North America and may be conspecific with A. rugulosa.

The coelomycete Acaroconium punctiforme gen. sp. nov. is described from four members of the lichen-forming family Acarosporaceae, three species of Acarospora and Sarcogyne regularis. The new fungus is characterized by pycnidial conidiomata with a distinct ostiolar collar, enteroblastic conidiogenesis, and the production of simple brown conidia. The separation of the fungus from other somewhat similar pycnidial fungi growing on lichens and plant material is discussed.

The new species, Polysporina frigida Kantvilas & Seppelt is described and illustrated. It is the first record of this genus from the Antarctic continent.