Arthonia epipolytropa Hafellner & Grube and Arthonia subclemens Hafellner, Grube & Muggia are described as new to science. Both are specific parasites of Lecanora polytropa s. lat., but of differing pathogenicity and of very different appearance. Whereas the clearly parasitic Arthonia epipolytropa with its agglomerated ascomata is presently known with certainty from a number of localities along the arch of the Alps (Austria, Italy, Switzerland), other parts of Europe (Norway, Albania) and northern America (USA), the less harmful A. subclemens with its isolated sunken ascomata is currently known only from a small number of localities in the Eastern Alps (Austria, Italy) and various mountain ranges in southern Europe (Spain, North Macedonia, Greece). The species are compared with other Arthonia species known from Lecanora or one of its recently segregated genera. A key to the fungi regularly found on Lecanora polytropa s. lat. is presented.

The genus Thelopsis was classified in the family Stictidaceae but its systematic position has never been investigated by molecular methods. In order to determine its family placement and to test its monophyly, fungal DNA of recent collections of Thelopsis specimens was sequenced. Phylogenetic analyses using nuLSU, RPB2 and mtSSU sequences reveal that members of Thelopsis form a monophyletic group within the genus Gyalecta as currently accepted. The placement of Thelopsis, including the generic type T. rubella, within the genus Gyalecta challenges the generic circumscription of this group because Thelopsis is well recognized by the combination of morphological characters: perithecioid ascomata, well-developed periphysoids, polysporous asci and small, few-septate ellipsoid-oblong ascospores. The sterile sorediate Opegrapha corticola is also placed in the Gyalectaceae as sister species to Thelopsis byssoidea + T. rubella. Ascomata of O. corticola are illustrated for the first time and support its placement in the genus Thelopsis. The hypothesis that O. corticola might represent the sorediate fertile morph of T. rubella is not confirmed because the species is phylogenetically and morphologically distinct. Thelopsis is recovered as polyphyletic, with T. melathelia being placed as sister species to Ramonia. The new combinations Thelopsis corticola (Coppins & P. James) Sanderson & Ertz comb. nov. and Ramonia melathelia (Nyl.) Ertz comb. nov. are introduced and a new species of Gyalecta, G. amsterdamensis Ertz, is described from Amsterdam and Saint-Paul Islands, characterized by a sterile thallus with discrete soralia. Petractis luetkemuelleri and P. nodispora are accommodated in the new genus Neopetractis, differing from the generic type (P. clausa) by having a different phylogenetic position and a different photobiont. Francisrosea bicolor Ertz & Sanderson gen. & sp. nov. is described for a sterile sorediate lichen somewhat similar to Opegrapha corticola but having an isolated phylogenetic position as sister to a clade including Gyalidea praetermissa and the genera Neopetractis and Ramonia. Gyalecta farlowii, G. nidarosiensis and G. carneola are placed in a molecular phylogeny for the first time. The taxonomic significance of morphological characters in Gyalectaceae is discussed.

A new species of Synarthonia, S. leproidica, is described from Luxembourg. Phylogenetic analyses of mtSSU and RPB2 sequences were used to determine the generic affiliation of this sterile species. Synarthonia leproidica differs from all other species of the genus by the combination of a leproid thallus and the production of psoromic acid. It is the sister species to S. muriformis in our phylogenetic analyses. The discovery of the new species suggests that other strictly sorediate lichen species might have been overlooked in Europe, even in intensely explored countries such as Luxembourg. Phylogenetic analyses further confirm the placement of Reichlingia anombrophila in the genus Reichlingia and of Synarthonia astroidestera in the genus Synarthonia. Arthonia atlantica is transferred to the genus Reichlingia as R. dendritica.

The genus Inoderma (Ach.) Gray is lectotypified with Inoderma byssaceum and resurrected for a small group of species in Arthoniaceae with elevated, white pruinose pycnidia, immersed to adnate white pruinose apothecia and a weakly gelatinized hymenium. Inoderma nipponicum is described from Japan, I. afromontanum from Uganda and the European Lecanactis subabietina is transferred to the genus. Sporodophoron is described for a small group of species in Arthoniaceae related to Inoderma but with a unique type of sporodochia instead of pycnidia. Sterile specimens of this new genus resemble species of Tylophoron but differ in the rounded angular to elliptical to short cylindrical, 0–2-septate sporodochial conidia with unevenly thickened walls which are formed apically in zigzag-shaped and occasionally branched chains. Sporodophoron further differs in thallus chemistry and is genetically distinct. Tylophoron americanum and Schismatomma cretaceum are transferred to Sporodophoron, and the new species S. gossypinum from Japan and S. primorskiense from eastern Russia are described. The genus Glomerulophoron is described for a single species from Mauritius, G. mauritiae, differing from Sporodophoron in the tightly coiled chains of sporodochial conidia and being genetically distinct. A phylogenetic tree showing the position of Inoderma, Sporodophoron and Glomerulophoron in Arthoniaceae is presented. A key to all species of Arthoniaceae with sporodochia or elevated white pruinose pycnidia is presented. Arthothelium spectabile, the type of the large heterogeneous genus Arthothelium, is confirmed for the cryptothecioid subclade in Arthoniaceae.

The new corticolous lichen species Bactrospora angularis is described from Brazil. It has apothecia that are usually irregular in outline and transversely (19–)28–35-septate, filiform ascospores (85–)120–150 × 5–7 μm with some constrictions. A revised world key is given to all currently known species of Bactrospora.

The type specimens of Synarthonia bicolor and S. stigmatidialis were examined, leading the authors to revise their descriptions as well as the generic description. Also, two new species of Synarthonia, viz. S. psoromica and S. sikkimensis are described from India. Synarthonia psoromica, collected from the Nilgiri Hills of Tamil Nadu, is characterized by immersed synascomata and the presence of psoromic acid. Synarthonia sikkimensis, collected from Sikkim-Himalaya, is characterized by the sorediate thallus with a rhizomorph-like prothallus. These distinguishing characters are observed for the first time in Synarthonia. After considering the protologue of the recently described S. sarcographoides, a comprehensive account of this genus is made. In addition, a world key to all known species of Synarthonia is provided.

Three new corticolous Arthoniaceae are described from the Chapada do Araripe, an isolated table mountain in the state of Ceará, in NE Brazil. Arthonia stipitata, lichenicolous on unidentified sorediate crusts, with red, tiny, stipitate apothecia, 3-septate ascospores, 10–12×3·0–3·5 µm. Stirtonia lucida with rather small ascigerous areas, lichexanthone and zeorin in the thallus, globose asci, ascospores 8 per ascus, ellipsoid, 17–19×8–10 µm, with occasionally some longitudinal septa. Stirtonia ochracea with rather small ochraceous ascigerous areas, thallus without secondary metabolites, ascospores 8 per ascus, (7–)9(–11)-septate, 47–55×14–20 µm. These species were found during a study aiming at an inventory of the lichen biodiversity of the Cerrado forests in the area, and were not found during earlier ecological studies in the Caatinga forests in the same area. Stirtonia lucida is the first species assigned to this genus which occasionally has some longitudinal septa in the ascospores. Such specimens might be confused with Cryptothecia species.

Eight species of Herpothallon are recorded from the Andaman Islands, four of which are described as new: Herpothallon coralloides, H. globuliferum, H. lutescens and H. minutum. All these new species have a non-pigmented thallus, prothallus, hypothallus and pseudisidia. Herpothallon coralloides and H. lutescens possess cylindrical pseudisidia whereas H. globuliferum and H. minutum have granular to globose pseudisidia. Herpothallon globuliferum is foliicolous. Herpothallon echinatum, H. granulare, H. granulosum and H. philippinum are reported for the first time from the Andaman Islands. A key to the Indian species is provided. Heiomasia pallescens (Graphidaceae), a byssoid taxon with a disc-shaped isidioid structure, is also described as new to science.

A corticolous lichen species, Opegrapha granulosa Siljo & G. P. Sinha, with a UV+ pale yellow thallus, is described as new to science from the Sundarbans Biosphere Reserve, West Bengal, India.

The new genus, Cameronia Kantvilas, is described and illustrated. It is characterized by a crustose thallus, a chlorococcalean photobiont, deeply immersed perithecioid ascomata, four-spored asci with an intensely hemiamyloid outer wall and non-amyloid, well-developed tholus, and hyaline, muriform ascospores. The taxonomic position of the new genus is uncertain although a relationship with the Ostropomycetidae is likely. Two species, both endemic to the highlands of Tasmania, are described: C. pertusarioides Kantvilas, which is one of the most common lichens on dolerite in alpine Tasmania, and C. tecta Kantvilas, which is confined to metamorphosed sediments.

Enterographa bengalensis, a new species is described from the mangrove reserve – Sundarbans Biosphere Reserve, West Bengal, India. It is characterized by the convergent punctiform to lirelliform ascomata, 12–15(–17) septate fusiform ascospores and the presence of psoromic acid. In addition, three species of the genus viz. E. anguinella (Nyl.) Redinger, E. divergens (Müll. Arg.) Redinger and E. multiseptata R. Sant. are also reported for the first time from India.

Fifty-six known lichenicolous, non-lichenized Opegrapha (Roccellaceae, Arthoniales) species (containing some undescribed taxa) are listed here, five of which are known from Caloplaca (Teloschistaceae, Teloschistales). Opegrapha vulpina, a new lichenicolous fungus on endolithic Caloplaca subg. Pyrenodesmia (Caloplaca erodens and rarely C. albopruinosa), is described from Europe. A second new species, Opegrapha hellespontica, lichenicolous on Caloplaca aurantia, is described from the European part of Turkey. Two possible sibling species of Opegrapha rupestris s. l. lichenicolous on Caloplaca cirrochroa and C. variabilis s. l., respectively, are discussed in the paper, but have not been described.

Enterographa brezhonega, a fourth lichenicolous species in the genus is described. The species has been collected in an ancient woodland in western France growing on Porina rosei and probably other crustose lichens with a Trentepohlia photobiont. It shows affinities with the similar Enterographa epiphylla, but has an even number of septa and short-lirelliform ascomata.

The first sorediate species in the genus Llimonaea, L. sorediata is described from coastal areas of western Europe. This new species is easily mistaken for Dirina massiliensis f. sorediata with which it often co-occurs. It grows on vertical or overhanging acidic cliffs. Fertile specimens were recently collected in Portugal. A description of the species together with notes on distribution, ecology and chemistry are provided and a key to the species of Llimonaea is also provided.

The new species Lichenostigma svandae is described. It is known exclusively from Acarospora cervina, where it forms black stromatic hyphal strands and black sack-shaped ascomata on the host thallus surface. It is similar to L. elongatum and L. rouxii, but differs in a few characters. A short overview of the known Lichenostigma species is provided.

Opegrapha species with muriform ascospores are revised and two species, differing only in the shape of their excipulum, are accepted: O. arabica, a widespread coastal species, and O. varians, known from mainland Yemen and Socotra. The genus Dictyographa, previously distinguished from Opegrapha by its muriform ascospores, is reduced into synonymy with Opegrapha. Dictyographa angolensis and D. sandwicensis are new synonyms of O. arabica; the type of D. cinerea was found to be a mixture of different species of the Hysteriaceae; and D. contortuplicata and D. psyllocarpa are excluded from the Arthoniales. Lectotypes are designated for D. angolensis, D. contortuplicata and D. sandwicensis.

A new species, Chrysothrix septemseptata, is described from India. It is characterized by 7-septate ascospores, which is unique within the genus. It is currently known only from the Sundarbans Biosphere Reserve, where it grows in mangrove plantations.

Bactrospora perspiralis, B. subdryina, Enterographa mesomela, Graphidastra laii and Lecanographa atropunctata (Roccellaceae) are described as new to science based on specimens collected in the wet subtropical lowlands of northern Thailand and Vietnam. The new Graphidastra is the third species in the genus and was also found in Taiwan.

A new species of Cryptothecia (Arthoniales, lichenized ascomycetes) is described from Northern Thailand. The species has been collected from planted mango trees at a single site in a rural area and is characterized by the punctiform soralia, soredia containing gyrophoric acid and 8-spored asci.

The sorediate variety of Sclerophytomyces circumscriptus (Taylor) Sparrius & P. James (Roccellaceae, Arthoniales) is described from sheltered, acid rock along Europe's western coasts and the Atlantic islands. This sorediate taxon is reported from the British Isles, Ireland, France, Spain, Portugal, the Azores and the Canary Islands. A description of the morphology, distribution and ecology is provided. The phylogenetic position of the new taxon is discussed, as well as nomenclatural and orthographic issues. The name Sclerophytomyces is proposed as an orthographic correction of the published name Sclerophytonomyces.