A revision of corticolous Mazosia specimens showed that four species are present, all differing from the foliicolous taxa in the genus. One of them is widely distributed in the tropics and the others are, as far as is known, neotropical. Three species are co-occurring in NE Brazil. They can be distinguished as follows: M. leptosticta (Nyl.) Sparrius has longer ascospores (22–35×4–7 µm) than the other species, M. endonigra A. A. Menezes, M. Cáceres & Aptroot sp. nov. has sessile apothecia on a smooth thallus and occasionally also sessile pycnidia, M. carnea (Eckfeldt) Aptroot & M. Cáceres comb. nov. has immersed apothecia and a smooth thallus, and M. viridescens (Fée) Aptroot & M. Cáceres comb. nov. has distinct verrucae on the thallus. Descriptions are given and an identification key is presented to all Mazosia species with 3-septate ascospores, which includes all corticolous species known so far.

The following new species of Arthoniales are described from Rondônia: Alyxoria fuscospora with 3-septate clavate ascospores of 20–23×4·5–5·5 µm having a gelatinous layer soon appearing evenly brown (also known from other tropical countries). Chiodecton complexum with discrete soralia, immersed apothecia in branched lines and 3-septate ascospores (26–)33–40×2·5–3·5 µm. Coniarthonia rosea, similar to C. pulcherrima but with the apothecia pink and more irregular in outline and the ascospores 13–16×5·5–6·5 µm. Cresponea flavosorediata with yellow-olive soralia, apothecia with yellow pruina and 7–9-septate ascospores, 26–38(–50)×5·0–6·5 µm. Cresponea lichenicola, lichenicolous on a Pyrenula, with 0·1–0·3 mm wide apothecia with yellow pruina. Eremothecella helicella with helicoid curved c. 17–29-septate conidia c. 70–95×2 µm long if uncoiled, with septa 3–6 µm apart. The Arthoniales are a speciose component of the lowland rainforest of Rondônia. A key is provided to the corticolous species of most groups of Arthoniales found in Rondônia. The foliicolous species found so far are listed. Most are new records for Rondônia. Chrysothrix occidentalis is new to the Neotropics.

Two new species of the small genus Crypthonia are described from the Chapada do Araripe, an isolated table mountain in the state of Ceará, in NE Brazil. Both share the thallus and ascoma organization with the other known species of the genus, and are mainly characterized by differences in ascospores and chemistry. Crypthonia lichexanthonica A. A. Menezes, M. Cáceres & Aptroot has 7-septate ascospores and contains lichexanthone in the thallus, and C. submuriformis A. A. Menezes, M. Cáceres & Aptroot has (sub)muriform ascospores and also contains lichexanthone, but only in the ascigerous areas. A key to all known species of the genus Crypthonia is provided, in which Crypthonia olivacea Frisch & G. Thor is newly reported from Argentina. The new species Syncesia byssolomoides A. A. Menezes, M. Cáceres & Aptroot is described from the same area. It also has a thin byssoid thallus, but differs by the narrowly fusiform ascospores and by containing psoromic acid. It differs from all Syncesia species by the absence of carbonization and the presence of psoromic acid. The epiphytic lichen flora in this Caatinga forest area is dominated by crustose lichens, with Graphis and Polymeridium as the most speciose genera.

The new species Opegrapha subdictyospora is described from NE Brazil. It is only the third species in the genus with (sub)muriform ascospores and is further characterized by the brown pruinose discs. It was collected at Vale do Catimbau National Park in Pernambuco, which is a Caatinga area, where it is locally common.

Lecanographa uniseptata is described as new to science. It is characterized by having small rounded to lirellate ascomata, and 1-septate ascospores. The species is known from tropical Africa (Gabon) and tropical America (Guatemala).

Bactrospora flavopruinosa F. Berger & Aptroot is described as a new lignicolous lichen from Bermuda, characterized by the yellow pruinose apothecia and filiform ascospores.

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.

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 Opegrapha cladoniicola, lichenicolous on the podetia of Cladonia ochrochlora, is described from Hawaii. It is the first known Opegrapha species found growing on Cladonia.