Detailed anatomical and chemical studies conducted on recent collections made in almost all suitable habitats on Réunion, a small remote tropical island in the Indian Ocean, yielded a surprising diversity in the widespread lichen genus Micarea (Pilocarpaceae, Lecanorales). Twenty-one species are recognized, including 13 described here as new to science. They are: Micarea alectorialica, M. bebourensis, M. borbonica, M. boryana, M. cilaoensis, M. hyalinoxanthonica, M. isidiosa, M. melanoprasina, M. pseudocoppinsii, M. pseudolignaria, M. sublithinella, M. takamakae and M. tenuispora. Notes on local ecology and important biogeographical features are also given and a key to the species is provided. Isidiiform areolae are reported for the first time in the genus (M. isidiosa and M. tenuispora), as well as the production of protolichesterinic and confluentic acids (M. sublithinella and M. takamakae, respectively). Two groups within the genus are species-rich on the island: the M. peliocarpa group with possibly 5 species, including 3 new to science, and the M. prasina group with 4 species, including 2 new to science. Micarea levicula is reported here for the first time since its description, and the status of the material that can be referred to M. micrococca s. lat. needs further study.

Six new Micarea species are described from Europe. Phylogenetic analyses, based on three loci, i.e. mtSSU rDNA, Mcm7 and ITS rDNA and ancestral state reconstructions, were used to evaluate infra-group divisions and the role of secondary metabolites and selected morphological characters on the taxonomy in the M.prasina group. Two main lineages were found within the group. The Micareamicrococca clade consists of twelve species, including the long-known M.micrococca and the newly described M.microsorediata, M.nigra and M.pauli. Within this clade, most species produce methoxymicareic acid, with the exceptions of M.levicula and M.viridileprosa producing gyrophoric acid. The M.prasina clade includes the newly described M.azorica closely related to M.prasina s.str., M.aeruginoprasina sp. nov. and M.isidioprasina sp. nov. The species within this clade are characterised by the production of micareic acid, with the exception of M.herbarum which lacks any detectable substances and M.subviridescens that produces prasinic acid. Based on our reconstructions, it was concluded that the ancestor of the M.prasina group probably had a thallus consisting of goniocysts, which were lost several times during evolution, while isidia and soredia evolved independently at multiple times. Our research supported the view that the ancestor of M.prasina group did not produce any secondary substances, but they were gained independently in different lineages, such as methoxymicareic acid which is restricted to M.micrococca and allied species or micareic acid present in the M.prasina clade.

A revision of the Lecanora saligna-group is provided, based on specimens mainly from western and central Europe. Four new Lecanora species related to L. saligna are described: L. calabrica, L. coppinsii, L. pseudosarcopidoides and L. subsaligna, as well as a new variety, L. albellula var. macroconidiata. The species treated have in common relatively short and ± curved or bacilliform conidia and/or isousnic acid as a secondary metabolite. Species without isousnic acid, containing exclusively filiform conidia are excluded. Notes on various types of conidia (macroconidia, microconidia, mesoconidia and leptoconidia), morphology, ecology, chemistry and distribution are given and a key to the treated species is provided. Detailed descriptions are presented for eight related species in order to highlight the distinguishing characters.

Detailed morphological and anatomical studies informed by molecular inferences with mtSSU as a marker revealed two new species of Micarea in Western Europe, both belonging to the core group of the genus, namely the M. prasina group: M. herbarum from the Netherlands and Poland and M. meridionalis from Portugal and Italy. Micarea herbarum looks like a small or depauperate M. denigrata but clearly differs by the lack of gyrophoric acid, while M. meridionalis is distinguished by its granular thallus and the production of micareic acid.

Morphological, anatomical, chemical and molecular data suggest that a relatively common lichenicolous coelomycete on Lecanora conizaeoides is conspecific with Phoma cytospora, previously known only from parmelioid lichens, and that further populations on Cladonia and Pertusaria belong to the same species. This species is distinguished from Phoma by several taxonomically important characters and obviously represents a previously unrecognized genus, for which the name Briancoppinsia is introduced. Phylogenetic analyses using nuLSU and mtSSU sequences of isolates obtained in pure culture suggest that the new genus belongs to the Arthoniaceae (Arthoniales). This is the first obligate lichenicolous, non-lichenized anamorph confirmed to belong to the Arthoniales based on molecular data.