The evolution of multicellularity paved the way for significant increases in biological complexity. Although multicellularity has evolved many times independently, we know relatively little about its origins. Directed evolution is a promising approach to studying early steps in this major transition, but current experimental systems have examined only a subset of the possible evolutionary routes to multicellularity. Here we consider egalitarian routes to multicellularity, in which unrelated unicellular organisms evolve to become a multicellular organism. Inspired by microbial syntrophies and lichens, we outline three such routes from a system of different species to an interdependent relationship that replicates. We compare these routes to contemporary experimental systems and consider how physical structure, the threat of invasion, division of labour and co-transmission affect their evolution.

A review of algal (including cyanobacterial) symbionts associated with lichen-forming fungi is presented. General aspects of their biology relevant to lichen symbioses are summarized. The genera of algae currently believed to include lichen symbionts are outlined; approximately 50 can be recognized at present. References reporting algal taxa in lichen symbiosis are tabulated, with emphasis on those published since the 1988 review by Tschermak-Woess, and particularly those providing molecular evidence for their identifications. This review is dedicated in honour of Austrian phycologist Elisabeth Tschermak-Woess (1917–2001), for her numerous and significant contributions to our knowledge of lichen algae (some published under the names Elisabeth Tschermak and Liesl Tschermak).

Using molecular data to delimit species or reconstruct their evolutionary history is now widely used across all organisms. However, such analyses can suffer from poor or false specimen identifications leading to incorrect conclusions. Here we show that the use of misidentified specimens in a phylogenetic framework resulted in questionable conclusions in a previously published study (Mark et al. 2016). Using morphological, chemical and statistical analyses on the specimens used in that study, we found support for Usnea barbata and U. dasopoga being morphologically and anatomically distinct species with separate clusters in the molecular phylogeny. Furthermore, our revision of specimen identifications refutes the synonymization of U. substerilis with U. lapponica. In conclusion, we discuss the issue of correct identification of voucher specimens in DNA databases and conclude with some general suggestions to avoid false specimen identifications in phylogenetic studies.

The genus Arthothelium A. Massal. in Tasmania comprises ten species. Five of these are described as new: A. bacidinum Kantvilas, a saxicolous, littoral species with subglobose apothecia, non-macrocephalic ascospores, 25−40 × 11−19 μm, and containing the pigment Endoaurantiacum-gold which yields a K+ red reaction; A. insolitum Kantvilas, lichenicolous in rainforest and characterized by subglobose apothecia, very large, non-macrocephalic ascospores, 50−80 × 22−40 μm, and containing the pigment Interveniens-brown which reacts K+ olive green; A. macounioides Kantvilas, corticolous in wet forest and characterized by sessile, convex apothecia, macrocephalic ascospores, 29−42 × 11−18 μm, and containing the pigment Endoaurantiacum-gold; A. magenteum Kantvilas, a common wet forest epiphyte with applanate apothecia, non-macrocephalic ascospores, 25−55 × 11−22 μm, and containing a unique maroon-red, K+ pink pigment; and A. subtectum Kantvilas, a saxicolous species with convex apothecia, macrocephalic ascospores, 22−36 × 9−14 μm, and containing Endoaurantiacum-gold. The New Zealand species A. endoaurantiacum Makhija & Patw. and A. suffusum (C. Knight) Müll. Arg., and the Australian A. velatium Müll. Arg. are recorded for Tasmania for the first time. The names A. obtusulum (Nyl.) Müll. Arg., A. pellucidum (C. Knight) Müll. Arg. and A. polycarpum Müll. Arg. are considered synonyms of the widespread A. ampliatum (C. Knight & Mitten) Müll. Arg. Arthothelium ferax Müll. Arg. is a synonym of A. interveniens (Nyl.) Zahlbr. and A. subspectabile Vĕzda & Kantvilas is a synonym of A. suffusum. The sole record of A. macrothecum (Fée) A. Massal. from Tasmania is found to be based on a misidentification. A key to the species is provided. The importance of apothecial pigments, apothecial morphology and ascospore septation is discussed, and three pigments are characterized by their appearance in water and other standard media.

Three species of lichenicolous Opegrapha s. lat. are newly described, all apparently host-specific at genus level. Opegrapha arthoniicola Coppins & S. Y. Kondr. is described from western Britain and Ireland, where it grows on the thallus of Arthonia radiata on Corylus bark; it has small clustered ascomata, asci that are usually 6-spored and rather small ascospores (10.5–)12.5–14.5 μm in length. Opegrapha sawyeriana Coppins occurs on the thallus of Coniocarpon cinnabarinum, also on Corylus bark, from oceanic western parts of Scotland, Ireland and southern England; in comparison to O. arthoniicola it has smaller, often scattered ascomata with a pigmented basal layer, 8-spored asci and slightly larger ascospores 13–14.5(–16) μm in length. Opegrapha hochstetteri Coppins has been found on thalli of Verrucaria hochstetteri and V. muralis on calcareous rocks and stonework in southern England and Luxembourg; collections were formerly identified as Opegrapha rupestris Pers. but it differs from this species by narrower ascomata with a persistent narrow slit, normally 6- rather than 8-spored asci and ascospores with pigmentation in the spore wall rather than the perispore. Lifted from synonymy is Opegrapha opaca Nyl., which inhabits the thallus of Verrucaria nigrescens and V. viridula on calcareous rocks and stonework, and is so far recorded from southern England, Luxembourg, France, northern Spain and Israel. The hosts of the European species of lichenicolous Opegrapha on Verrucaria s. lat. on calcareous rocks (O. hochstetteri, O. opaca and O. rupestris) belong to different phylogenetic lineages within the Verrucariaceae. A key is also provided to the lichenicolous species of Opegraphaceae currently known from Great Britain and Ireland.

The new genus Australidea Kantvilas, Wedin & M. Svensson is described to accommodate Lecidea canorufescens Kremp., a widespread lichen in temperate Australasia. It is characterized by a crustose thallus with a green photobiont, reddish brown, biatorine apothecia with an internally hyaline, cupulate proper exciple constructed of branched and anastomosing hyphae, mainly simple paraphyses, 8-spored, Porpidia-type asci and simple, hyaline, non-halonate ascospores. A phylogenetic analysis places the new genus in the family Malmideaceae. Lecidea canorufescens Kremp., L. glandulosa C. Knight, L. immarginata R. Br. ex Cromb. and L. intervertens Nyl. are lectotypified. These names, plus L. dacrydii Müll. Arg. and L. eucheila Zahlbr., are all synonyms of Australidea canorufescens (Kremp.) Kantvilas, Wedin & M. Svensson comb. nov. Several genera superficially similar to Australidea, including Malcolmiella Vĕzda, Malmidea Kalb et al. and Myochroidea Printzen et al., are compared. A comprehensive anatomical and morphological description of the genus Malcolmiella, recorded for Tasmania for the first time, is also provided. The new combination M. interversa (Nyl.) Kantvilas, Wedin & M. Svensson is introduced and the names M. cinereovirens Vĕzda and M. cinereovirens var. isidiata Vĕzda are reduced to synonyms. The systematic position of this genus remains unclear, although phylogenetic analysis suggests its affinities lie with a group of genera that includes Bryobilimbia Fryday et al., Romjularia Timdal and Clauzadea Hafellner & Bellem.

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.

Gibbosporina cyanea is described here as new to science, based on its holotype collected in Sri Lanka in the 1860s. The species is a bipartite cyanolichen in contrast to all other known Gibbosporina species, which are tripartites. The species appears to have evolved through cephalodia emancipation followed by divergence. Phyllidia indicate a cephalodiate evolutionary origin with a continued function similar to vegetative propagules. The species is considered to represent a relatively young speciation within an evolutionary old genus and G. sphaerospora is discussed as a possible candidate for being its closest known relative based on spore morphology. As the species appears to be so different from the remaining Gibbosporina species, it is compared here to representatives of other related palaeotropical cyanogenera, such as Leightoniella, Lepidocollema, Pannaria and Physma. Perispore structure is shown to be a useful character in separating these genera, including distinct clades of the non-monophyletic genera Physma and Lepidocollema. Leightoniella zeylanensis is reported here as new to Japan, and it is concluded that Pannaria lurida needs to be restudied in India and Sri Lanka.

In recent years, several species that have long been considered to belong in Bacidia s. lat. have been transferred to other genera such as Bellicidia, Bibbya, Scutula, and also to Toniniopsis, accommodating species previously placed in Bacidia and Toninia. One of its widespread species, Toniniopsis subincompta, can be recognized by its thinly granular thallus, dark brown to black apothecia, green epithecium, red-brown hypothecium, and bacilliform ascospores. However, it shows considerable variation in thallus structure, and coloration of apothecia, hypothecium and exciple. We sequenced 20 specimens of T. subincompta to investigate whether there is phylogenetic support for the delimitation of species in accordance with the variability of the observed characters. For phylogenetic analyses, we used newly generated sequence data from the nuclear internal transcribed spacer (nrITS), mitochondrial small subunit (mtSSU) and DNA-directed RNA polymerase II subunit (RPB2). Maximum likelihood and Bayesian inference analyses, as well as three species delimitation programs, provided consistent evidence that T. subincompta forms two separate lineages, to be recognized at the species level. The complex nomenclature of T. subincompta (basionym Lecidea subincompta) shows it to be a synonym of Bellicidia incompta. For the most common taxon previously called Bacidia (Toniniopsis) subincompta, the new combination T. separabilis is made, rather than proposing a conserved type for Lecidea subincompta. Toniniopsis dissimilis is newly described to accommodate the less common taxon. Toniniopsis dissimilis is characterized by a predominantly wrinkled to warted to subsquamulose thallus; generally grey-brown to dark brown apothecia, often with a lighter margin; a dark brown hypothecium, frequently gradually merging into the coloration of the exciple below and the lateral part of the exciple attached to the hymenium; a mostly colourless rim and lateral part of the exciple. The closely related T. separabilis is characterized by a thallus of mostly single or contiguous ±loose granules, often forming short, coralloid, isidium-like bulges; darker apothecia, with a margin mostly of the same colour or darker than the disc; a comparatively thinner hypothecium easily separated from the exciple below. The rim and lateral part of the exciple often contain either a blue, brown or mixed blue-brown colour in the upper part or along the whole margin. Lectotypes of Bacidia vegeta, Lecidea bacillifera f. melanotica and Secoliga atrosanguinea var. affinis (the synonyms of T. separabilis) are selected. Cyanotrophy and the occurrence of albino morphs in T. separabilis are discussed.

Ramalina arsenii sp. nov. belongs to the R. pollinaria group and is easily recognized by its ITS barcode and several micro-morphological characters that are diagnostic in a European context: small size, less than 3 cm long; soralia developing on the underside of lobe apices; absence of excavate depressions on the lower side. Its ecological niche (i.e. rock outcrops and especially underhangs of slightly calcareous rocks, at low and mid altitudes) is also unique. Ramalina arsenii is frequent and locally abundant in France (Alps, Cantal) and Switzerland (western Alps), and is also known from Germany and the Spanish side of the Pyrenees.

To clarify deep relationships among species lineages within Bacidia s. str., and to investigate the robustness of the deeper branches, we combined data from three traditionally used RNA-coding genes (nrITS, nrLSU and mtSSU) with two protein-coding genes (RPB1 and RPB2). The multigene phylogeny contained 48 newly generated sequences from the Russian Far East and all Bacidia s. str. sequences from GenBank (131 sequences). We subjected the alignments for the single and concatenated data sets to Bayesian inference (BI) and two maximum likelihood (ML) analyses (RAxML and IQ-TREE). The topologies of phylogenetic trees recovered from BI and ML analyses were highly concordant. The multilocus phylogeny of Bacidia s. str. was congruent with previous results based on nrITS sequences from the Russian Far East but with considerably higher support values for most of the deeper branches. A correlation between the recovered clades and apothecial pigments in the upper part of the hymenium and lateral exciple was observed. Based on morphological and molecular evidence, Bacidia obtecta is described as new to science. It was recovered as the sister lineage of B. elongata. The two species are alike in having up to four enlarged lumina cells along the exciple edge, but B. obtecta differs in the abundant crystals found in the upper hymenium and lateral exciple, and by having spores with fewer septa.

The new genus Sinuicella, an early successional lichen, was found on bare soil in Oregon, USA. The thallus is minute fruticose, grey to nearly black, branching isotomic dichotomous, branches round, 20–90 μm wide in water mount. The cortex is composed of interlocking cells shaped like jigsaw puzzle pieces. Spores are hyaline, 1-septate, 25–40(–50) × 6.5–9(–11) μm. Maximum likelihood phylogenetic analyses on multilocus data sets, first spanning the entire order Peltigerales and then restricted to Peltigeraceae with extended sampling from Solorina and Peltigera, revealed the placement of Sinuicella outside of currently recognized genera, sister to Peltigera, with high support. Based on the phylogenetic, morphological and ecological distinctness of Sinuicella, we formally introduce a new genus represented by the single species S. denisonii. The cyanobiont of S. denisonii is Nostoc from phylogroup XL, Clade 2, Subclade 3 based on the rbcLX marker.

Lichens often grow in microhabitats where they are exposed to severe abiotic stresses such as desiccation and temperature extremes. They are also often exposed to levels of light that are greater than lichen photobionts can use in carbon fixation. Unless regulated, excess energy absorbed by the photobionts can convert ground state oxygen to reactive oxygen species (ROS). These ROS can attack the photosynthetic apparatus, causing photoinhibition and photo-oxidative stress, reducing the ability of the photobionts to fix carbon. Here, we outline our current understanding of the effects of high light on lichens and the mechanisms they use to mitigate or tolerate this stress in hydrated and desiccated states. Tolerance to high light can be achieved first by lowering ROS formation, via synthesizing light screening pigments or by thermally dissipating the excess light energy absorbed; second, by scavenging ROS once formed; or third, by repairing ROS-induced damage. While the primary focus of this review is tolerance to high light in lichen photobionts, our knowledge is rather fragmentary, and therefore we also include recent findings in free-living relatives to stimulate new lines of research in the study of high light tolerance in lichens.

Three species of the family Teloschistaceae (lichenized Ascomycota) are described as new to science from Southern and Eastern Siberia and the Far East. Corticolous Caloplaca saviczii belongs to the genus Caloplaca s. str.; it has C. cerina-like apothecia and green to grey-green, crateriform soralia with a white rim. Lendemeriella aureopruinosa is a saxicolous taxon with a thin grey thallus and small apothecia 0.3–0.6 mm in diameter, with a dark orange disc usually bearing epipsamma and often with a grey true exciple containing the pigment Cinereorufa-green. Orientophila infirma is a corticolous species with an endophloeodal thallus and small orange apothecia, 0.2–0.3 mm in diameter, usually with an inconspicuous thalline exciple. All new taxa presumably have a boreal north-eastern distribution in Asia.

A new fruticulose species, Polycauliona comandorica, is described from the supralittoral zone of the Commander Islands in the Russian Far East. This growth form is very rare in the family Teloschistaceae where the new species belongs. It is the only fruticulose species of the family that forms vegetative propagules (soredia and blastidia). Polycauliona comandorica is similar to the North American P. thamnodes but differs in having a lighter yellow to grey thallus, longer and thicker branches with a rough surface, soredia and blastidia, and in lacking apothecia. Two fruticulose-lobate pairs of species in Polycauliona are briefly discussed: P. comandorica-P. verruculifera and P. thamnodes-P. brattiae.

Non-photochemical quenching (NPQ) plays an important role in protecting photosynthetic organisms from photoinhibition by dissipating excess light energy as heat. However, excess NPQ can greatly reduce the quantum yield of photosynthesis at lower light levels. Recently, there has been considerable interest in understanding how plants balance NPQ to ensure optimal productivity in environments in which light levels are rapidly changing. In the present study, chlorophyll fluorescence was used to study the induction and relaxation of non-photochemical quenching (NPQ) in the dark and the induction of photosynthesis in ten species of lichens, five sampled from exposed and five sampled from shaded habitats. Here we show that the main difference between sun and shade lichens is the rate at which NPQ relaxes in the dark, rather than the speed that photosynthesis starts upon illumination. During the first two minutes in the dark, NPQ values in the five sun species declined only by an average of 2%, while by contrast, in shade species the average decline was 40%. For lichens growing in microhabitats where light levels are rapidly changing, rapid relaxation of NPQ may enable their photobionts to use the available light most efficiently.

An examination of collections from Japan has increased the number of Brianaria and Micarea species known from that country from eight to 19, including one new species, M. rubioides Coppins (also from Malaysia and the Philippines). Eleven species are reported as new to Japan (M. botryoides (Nyl.) Coppins, M. denigrata (Fr.) Hedl., M. erratica (Körb.) Hertel et al., M. hedlundii Coppins, M. lithinella (Nyl.) Hedl., M. micrococca (Körb.) Gams ex Coppins and M. misella (Nyl.) Hedl.) or new to Asia: M. byssacea (Th. Fr.) Czarnota et al., M. deminuta Coppins and M. xanthonica Coppins & Tønsberg (new to Asia; Japan); M. nitschkeana (J. Lahm ex Rabenh.) Harm. (new to Asia; South Korea). The presence of Micarea prasina s. str. from Japan needs to be confirmed; no collection was found in this study. Additional collections from South Korea and Sri Lanka are also reported, including the new species M. ceylanica Coppins from Sri Lanka. The identity of M. synotheoides (Nyl.) Coppins, originally described from Japan, has been resolved, resulting in the renaming of Western European material, previously under that name, as M. longispora Coppins. Micarea coreana Lőkös et al. is reported here as a synonym of M. erratica. The type of Lecidea inopinula Nyl. requires the new combination Micarea inopinula (Nyl.) Coppins & T. Sprib. to replace Micarea prasinella (Jatta) I. M. Lamb.