Peter D. Crittenden served as senior editor of The Lichenologist, the flagship journal in the field of lichenological research, for a period of two decades, between 2000 and 2019. A review of the development of the journal and the publication output during this period is provided. The number of papers published during this period (1197) matches that of all papers published under the three previous senior editors, Peter W. James, David L. Hawksworth and Dennis H. Brown, during a much longer period of 42 years from 1958 to 1999. Peter oversaw important editorial changes to the layout and content of the journal: an increased size with a modern cover design, leaving behind the classic mint-coloured cover of more than 40 years; the addition of ‘thematic issues’ and encouragement of large monographs; implementation of substantial changes to the Code, such as effective electronic publication and obligate registration of new fungal names; and more recently a new policy to reject so-called ‘single naked species descriptions’. Shortly before Peter took over as senior editor, The Lichenologist had received its first impact factor, and Peter managed to continuously increase this measure from around 0.9 to lately up to over 1.5, higher than most other competing journals. The 1197 papers between 2000 and 2019 were published by a total of 1138 different authors, more than half of whom appeared just once as author, whereas a small number participated in numerous (up to 93) papers. There was a continuous increase in the mean number of authors per paper per year, from below 2.5 to around 3.5, the highest numbers ranging between 11 and 30; still, c. 75% of all papers between 2000 and 2019 were single-authored or had up to three authors. Based on affiliations at the time of publication, two thirds of author contributions came from Europe (66%), 13% from North America, 9% from Asia and 7% from Latin America. Likewise, almost half of the study areas were located in Europe and around 10% each in North America, South America and Asia. The countries with the highest number of studies included, in descending order, the United States, Spain, the United Kingdom, Norway and Sweden. North America and Europe were over-represented in terms of author contributions, whereas Africa, Latin America, Australia and Oceania were over-represented in terms of study areas. The 1197 papers analyzed encompassed a broad diversity of topics, classified into 32 categories. Taxonomy of lichenized fungi was the most frequent component, representing the focal point in almost half of all studies, followed by phylogeny and evolution, ecology, and the taxonomy of lichenicolous fungi. Around two thirds of the currently accepted genera of lichenized fungi were treated, with a significant correlation between known species richness and the number of papers in which a genus was treated, underlining the taxonomic representativity of papers published in the journal during the past two decades. Examples of genera that were treated more frequently than expected included commonly studied model organisms, such as Lobaria, and those frequently featured in ecological or other non-taxonomic studies, such as Xanthoria. Species-rich tropical genera, particularly in the Graphidaceae, were generally under-represented. Mean number of authors per paper per volume and total number of country origins of authors per volume were the best predictors of impact factor, followed by diversity of study countries per volume, mean number of study countries per paper per volume, mean number of topics per paper per volume, and proportion of studies with phylogenetic components per volume. Individual papers that contributed to high impact factors included broad-scale revisionary treatments and worldwide keys to species-rich taxa, substantial phylogenetic reclassifications of known taxonomic groups, papers dealing with novel methodological approaches of broad interest, and broad-scale studies related to environmental change and lichen biomonitoring.

The new species Caloplaca tswaluensis is described from Tswalu Kalahari Reserve, Northern Cape Province, South Africa. Caloplaca tswaluensis occurs on the trunks of Vachellia erioloba (camelthorn) trees and is characterized by its 3-septate to quadrilocular ascospores. Molecular data indicate that the new species is placed in the subfamily Teloschistoideae but cannot be assigned to any existing genus and, because its systematic position is unclear, we choose to describe it in Caloplaca s. lat. Caloplaca tswaluensis is compared with other crustose Teloschistaceae species with plurilocular ascospores.

Hypogymnia papilliformis McCune, Tchabanenko & X. L.Wei is described as a new species of lichenized fungus from the Primorsky region of Russia and Shaanxi Province in China. It is a relatively rare species from mixed conifer-broadleaved forests in suboceanic climates, in mountainous areas at elevations of 600–1500 m. Most similar to H. delavayi, the species are distinguished by branching pattern and chemistry. Hypogymnia papilliformis is predominantly isotomically branched while H. delavayi usually develops subpinnate branching. The ceiling of the lobe cavity is mid brown to dark brown in H. papilliformis, while the ceiling is often pale brownish or white in H. delavayi. Also, H. papilliformis lacks 3-hydroxyphysodic acid, and thus has a K– medulla, while H. delavayi always contains 3-hydroxyphysodic acid as a major substance and is thus K+ slowly reddish brown. We provide a key to the six esorediate Hypogymnia species known from the Russian Far East.

In recent years, the genus Bryoria (Parmeliaceae, Lecanoromycetes) has been the subject of considerable phylogenetic scrutiny. Here we used information on six gene regions, three nuclear protein-coding markers (Mcm7, GAPDH and Tsr1), two nuclear ribosomal markers (ITS and IGS) and a partial mitochondrial small subunit (mtSSU), to examine infrageneric relationships in the genus and to assess species delimitation in the Bryoria bicolor/B. tenuis group in section Divaricatae. For this purpose, phylogenetic analyses and several of the available algorithms for species delimitation (ASAP, GMYC single, GMYC multiple and bPTP) were employed. We also estimated divergence times for the genus using *BEAST. Our phylogenetic analyses based on the combined data set of six gene loci support the monophyly of sections Americanae, Divaricatae and Implexae, while section Bryoria is polyphyletic and groups in two clades. Species from Bryoria clade 1 are placed in an emended section Americanae. Our study reveals that section Divaricatae is young (c. 5 My) and is undergoing diversification, especially in South-East Asia and western North America. Separate phylogenetic analyses of section Divaricatae using ITS produced a topology congruent with the current species concepts. However, the remaining gene regions produced poorly resolved phylogenetic trees and the different species delimitation methods also generated highly inconsistent results, congruent with other studies that highlight the difficulty of species delimitation in groups with recent and rapid radiation. Based on our results, we describe the new species B. ahtiana sp. nov., characterized by its bicolorous, caespitose, widely divergent thallus, conspicuously thickening main stems, well-developed secondary branches, and rather sparse third-order branchlets. Another new lineage, referred to here as B. tenuis s. lat., is restricted to western North America and may represent a new species recently diverged from B. tenuis s. str., though further work is needed.

Three name changes are proposed for the lichen checklist. Caloplaca heppiana should be called C. flavescens (Huds.)Laundon comb. nov. It is suggested that Coelocaulon muricatum (Ach.)Laundon comb. nov. is a more appropriate name for C. aculeatum subsp. hispidum. The name Schismatomma virgineum should be replaced with S. cretaceum (Hue)Laundon comb. nov.

Samples of Cladonia mitis were collected from three microhabitats within an open field in eastern Hokkaido, Japan. Two sets of sample thalli were taken in close proximity to geothermal vents and a third from a neighbouring area not directly affected by outgassings. Enzymes were extracted and separated by isoelectric focusing, and multiple enzyme forms of three oxidoreductases, glucose-6-phosphate dehydrogenase, glutamate dehydrogenase and superoxide dismutase, and two hydrolases, esterase and alkaline phosphatase, were examined. Similarities between microhabitats based on electrophoretic results were calculated using Jaccard's similarity coefficient and expressed graphically through the complementary techniques of clustering and ordination. All of the major differences in isozyme patterns between remote samples and those near fumaroles were in the two highly polymorphic enzymes, esterase and alkaline phosphatase. Differences were as great or greater than those between geographically separated conspecific populations of lichens examined previously. In the more sulphurous microhabitats, nine bands were much more frequent and eight much less so than in locations further from the source of gases.

Macentina aurantiaca sp. nov. (Verrucariaceae) is described from the Burren, western Ireland. A sciophilous lichen, it is characterized by its comparatively large, orange ascomata and by its mostly 7-septate, elongate-ellipsoid ascospores.

Gyalidea cylindrical is described as new, living on pleurocarpic epiphytic mosses in shaded situations.Gyalidea phyllophila is recorded for the first time in Europe. Both of them have been collected in the French Atlantic Pyrénées.

The new species Ochrolechia splendens Lumbsch and Messuti, is described from Mexico, south-western North America, where it occurs on exposed siliceous rocks. It is characterized by relatively large apothecia with entire margins, the presence of the gyrophoric acid chemosyndrome in the thallus and apothecial disc and the presence of lichexanthone as major components.

Verrucaria aranensis McCarthy and V. knowlesiae McCarthy are described as new from limestone in western Ireland. Verrucaria mulabilis Borrer is an illegitimate name; moreover, a number of British specimens attributed to it are V. dolosa Hepp. A key to minute-spored, terrestrial saxicolous Verrucariae is provided in which V. subumbrinula Vainio and V. anzianoides Magnusson are reduced to synonymy under V. naeviformis Vainio and V. arctica Lynge, respectively.

Chaenotheca degelii sp. nov. is described from New Zealand. The position of the species in the genus and the chemistry are discussed briefly. Chaenotheca degelii is a lignicolous species mainly occurring in the Central Plateau of North Island, but one isolated occurrence in the South Island is also known.