Environmental DNA (eDNA) offers significant potential to expand biodiversity monitoring, and recent efforts in obtaining eDNA by different sampling methods, including bulk samples of air, mixed vegetative material and stem flow, have broadened the opportunities for its use. However, identification of sequences from eDNA data is based on using so-far incomplete reference databases of catalogued DNA barcodes. In lesser-studied groups, such as lichens, the use of eDNA may therefore introduce biases relating to variable representation in barcode databases according to geography, growth form, ecology and conservation status. To understand these biases, we focused our study on a simple question, regionally targeted but thematically broad: how many British lichens have catalogued DNA barcodes usable as reference data for eDNA detection? Since sequence data is also stored across many different databases, our research focused on combining sources while addressing taxonomic changes. This British lichen-fungi perspective highlights critical challenges. We show that a substantial gap exists between sequenced species and those listed in the British Isles, meaning eDNA cannot currently provide a representative picture of lichen diversity. This is concerning because eDNA work is increasingly advocated for lichen survey and monitoring, and is becoming privatized and sold as a product, where methods and pipelines are made proprietary and hidden from peer review. In this study, we offer a warning at a time when the rapid uptake and application of eDNA and interpretation of its results remain subject to complex uncertainties. Looking towards the full potential of eDNA for lichen diversity monitoring, we outline species to target for nearing a more complete ITS reference database for British lichen diversity and suggest that taxonomic experts adopt approaches that can explicitly refine our knowledge on the current limitations of eDNA to direct future research agendas towards its more effective use.

Graphis epigraphis is described from Colombia as only thesecond, genuinely lichenicolous species in theGraphis-Allographa complex inGraphidaceae. It grows on species ofGraphis s. str., thus far found on thalli of G.leptoclada and G. pinicola. The new species ischaracterized by the lirellate ascomata forming delicate, stellately branchedpatches on the host, the entire, black labia laterally covered by a thinthalline margin formed by the host thallus, the laterally carbonized excipulum,and mostly 5-septate ascospores. The only other lichenicolous species known inthis complex, Allographa pauciloculata, differing in itscompletely carbonized excipulum and partly submuriform ascospores, grows onthalli of A. anomala and is known from Great Britain, whereasG. epigraphis was found in the tropical dry forest regionof the Magdalena Valley in Colombia. We performed morphology-based phylogeneticbinning to confirm the genus-level placement of both species inGraphis and Allographa, respectively. Acomparative survey of lichenicolous Graphidaceae andGomphillaceae (Graphidales) is given.

The family Trypetheliaceae is a diverse lineage of crustose lichenized fungi occurring almost exclusively in the tropics. Based on material collected in eastern Colombia in the region of the so-called Piedemonte Llanero, we describe here a new species for this family, in the genus Marcelaria, the fourth species known in the genus. The new species, Marcelaria casanarensis, is characterized by a clear hamathecium and large ascospores, similar to the neotropical M. purpurina, but it produces orange instead of red superficial pigmentation, outwardly agreeing with the two paleotropical species, M. benguelensis and M. cumingii. The new species thus appears to provide a morphological link between the currently known neotropical and paleotropical taxa. However, the pigment chemistry is closer to that of M. purpurina, so the orange colour is to be interpreted as homoplasy. Phylogenetically, based on an analysis of two markers, M. casanarensis and M. purpurina are closely related but M. casanarensis differs in two larger insertions in two different regions of the mitochondrial small subunit rDNA (mtSSU). A key to the four species currently accepted in Marcelaria is presented.

The foliicolous lichenized species Aspidothelium coronatum is described as new to science. The lichen was collected in the East Kameng district of Arunachal Pradesh, India and is characterized by submuriform ascospores. The novel taxon differs by displaying a corona of lobes around the perithecia, larger ascospores 80–105 × 14–22 μm in size, with 15–17 transverse septa and 1–2 longitudinal septa per segment. A worldwide key to all currently recognized species of Aspidothelium is provided.

We present a first comprehensive treatment of the foliicolous lichen biota of Brunei (Brunei Darussalam), a country c. 5765 km2 in size located on the northern coast of the island of Borneo. Based on a study of numerous leaves collected from 18 sites, resulting in 1745 individual collections, we identified 193 species in the material, including 21 new to science, raising the number of foliicolous lichens known from Brunei from 27 to 199 taxa. This is one of the highest numbers reported for single countries, after Brazil (455 species), Costa Rica (435), Ecuador (365), Mexico (340), Guyana (296), Australia (238), Bolivia and Colombia (228 each), and Papua New Guinea (213). However, relative to log-transformed area size, Brunei is one of the countries with the highest known foliicolous lichen diversity, having almost half the number of species as Costa Rica within an area little more than 10% of the size of the latter. The foliicolous lichen biota of Brunei has a dominant paleotropical element, clustering with that of Indonesia, Malaysia, the Philippines, Papua New Guinea and Australia. The newly described species are: Arthonia concentrica sp. nov., differing from A. trilocularis in the circular thallus with concentrically arranged, thinly pruinose ascomata; Arthonia flavirugosa sp. nov., differing from A. flavoverrucosa in the delicate, light yellowish ridges and the smaller ascospores; Arthonia tenuilobata sp. nov., differing from A. lobulicarpa in the more delicate lobes, pruinose ascomata and the brown ascospores; Byssolecania fumosocaerulea sp. nov., differing from B. fumosonigricans in the greyish blue outer fringe of the apothecia; Byssoloma inconspicuum sp. nov., differing from B. microcarpum in the dark brown apothecial disc and the excipulum lacking crystals; Byssoloma incrustatimurinum sp. nov., differing from B. murinum in the shorter, non-tapering ascospores and the crystals in the excipulum; Byssoloma subaeruginosum sp. nov., differing from B. usambarense in the dark aeruginous hypothecium and the (olive-)brown thallus; Chroodiscus lirellicarpus sp. nov., differing from C. argillaceus in the lirellate apothecia; Chroodiscus minutus sp. nov., differing from C. argillaceus in the very small apothecia; Echinoplaca septemseptata sp. nov., differing from E. tetrapla in the 7-septate ascospores; Eremothecella rugosa sp. nov., differing from E. calamicola in the ridged thallus and the longer conidia; Eremothecella verrucispora sp. nov., differing from E. calamicola in the brown, ornamented ascospores with more numerous septa; Fellhanera tutongensis sp. nov., differing from F. microdiscus in the 3–7-septate, more elongate, narrower ascospores; Mazosia bambusiradiata sp. nov., differing from M. bambusae in the radiately arranged thallus verrucae; Mazosia rugosa sp. nov., differing from M. pseudobambusae in the rugose instead of verrucose thallus surface; Ocellularia andulauensis sp. nov., differing from O. daniana in the more delicate, foliicolous thallus and the much smaller ascospores; Opegrapha albomarginata sp. nov., differing from all other species of Opegrapha with goniocystangia, in the white margin of the goniocystangia; Phylloporis verrucosula sp. nov., differing from P. palmae in the small perithecia and comparatively narrow ascospores; Porina riparia sp. nov., differing from P. pseudoapplanata [= Phyllophiale viridis] in the finely laciniate thallus with non-radiating photobiont; Spinomyces rubrotrichoides sp. nov., differing from other species in the genus in the multiseptate, worm-like ascospores and from Rubrotricha helminthospora, with which it agrees in ascospore type, in the entirely whitish, more delicate sterile thallus setae; Trichothelium subrobinsonii sp. nov., differing from T. robinsonii in the consistently 7-septate ascospores. The following three species are new continental records: Bapalmuia pallescens (Paleotropics), Lyromma palmae (Paleotropics), and Tapellaria major (Paleotropics). We also include two keys: one to foliicolous species of Arthonia with 2-septate, pigmented ascospores and one to foliicolous species of Porina with Phyllophiale-type isidia.

The crustose cyanolichen Fuscopannaria frullaniae (syn. Moelleropsis nebulosa subsp. frullaniae) is a poorly understood taxon that occurs on mosses and liverworts, described from eastern Canada and reported from the Iberian Peninsula, Macaronesia and the eastern USA. Originally placed in the genus Moelleropsis, the position of the species has been debated in the absence of sexual fruiting structures and, until now, DNA sequences from the fungal symbiont. We produced nine sequences from two fungal ribosomal loci from F. frullaniae collected at five different localities in Nova Scotia, Canada and North Carolina, USA. Initial BLASTn queries against public databases revealed high similarity between these sequences and basidiomycete sequences from the Dictyonema clade in Hygrophoraceae, specifically from the genus Acantholichen. We did not obtain ascomycete sequences from any locus or specimen. Phylogenetic analyses recovered the obtained sequences within the broader Acantholichen clade. We conclude that the lichen fungal symbiont is in fact a basidiomycete and introduce for it the new combination Acantholichen frullaniae. Acantholichen frullaniae is the first species of the genus to possess a granular, crustose thallus. The species lacks the characteristic, spiny, balloon-shaped cells called acanthohyphidia that are found in other species of the genus, though it possesses similar, albeit spineless cells on the surface of thallus granules; we suggest that these structures within the wider genus are homologous and represent spiny or smooth cystidia. Numerous samples yielded evidence of basidiospores and basidia produced from thallus granules, evident only after treatment with diluted potassium hydroxide, representing the first sexual structures reported in the genus. We discuss the possible reasons for this, as well as the ecology and threats to the species across its Canadian populations.

The genus Scoliciosporum includes crustose lichens characterized by gelatinized, branched and anastomosing paraphyses, Lecanora-type asci, and hyaline, usually septate ascospores. During investigations of crustose lichens in the Canadian Arctic, we discovered a distinctive, previously undescribed species of the genus occurring on terricolous bryophytes, an unusual substratum for the genus. Scoliciosporum quajautik is further characterized by its well-developed thallus, large apothecia with a persistent margin, fusiform 0–1-septate ascospores, and a pigmented hypothecium that produces a magenta effusion with potassium hydroxide solution. Phylogenetic analyses based on four loci (mtSSU, LSU, ITS and RPB2) place the species within a well-supported Scoliciosporum clade, confirming its generic placement despite its atypical morphology and ecology. The new species is currently known from five collections from Nunavut and northern Québec, all from lichen-rich tundra near the boundary between the Northern and Southern Arctic ecozones. In addition, we discuss the status of Catillaria muscicola and Stereocaulon cumulatum in the North American Arctic and conclude that Catillaria muscicola is known only from the type collection from Greenland whereas Stereocaulon cumulatum is present and probably widespread.

Lichens have been shown to optimize their photosynthetic apparatus in response to seasonal changes in light and temperature. However, there have been few investigations on seasonal variations in the biochemical mechanisms used by lichen photobionts to protect themselves against the potentially harmful effects of high light. In our earlier work, carried out during the summer months, we showed that Afromontane lichens collected from shaded habitats display higher values of non-photochemical quenching (NPQ) and lower maximum relative electron transport rates (rETRMAX) than thalli collected from sunny habitats. Here we employ chlorophyll fluorescence to show that, in contrast, winter collections of the Afromontane lichens Ramalina celastri and Usnea undulata from a diversity of sites display no significant differences in NPQ and rETRMAX between sun and shade forms. Results suggest that in the winter, shade forms downregulate their NPQ because loss of leaves causes less fluctuation in light levels, but retain similar values of rETRMAX to those of summer collections. Conversely, during the winter, thalli from exposed microhabitats downregulate their rETRMAX, presumably to reflect reduced possibilities for carbon fixation, and retain generally low values of NPQ. All winter collections display similar, high values of cyclic electron flow (CEF) and pseudocyclic electron flow (PCEF), indicating strong photoprotection of photosystem I. Taken together, the results suggest that photobionts can flexibly adjust their photosynthetic apparatus to seasonal variations in light availability.

Based on the review of specimens of the genus Bulbothrix s. lat. supported by morphological and chemical evidence, Bulbothrix buapana is described as a new species collected from a tropical dry forest in Oaxaca, Mexico. It differs from other species of Bulbothrix by having coronate apothecia, the presence of ciliate bulbs all over the upper cortex including the amphithecia, and by containing gyrophoric acid as the main medullary substance. Additionally, B. bulbillosa is reported for the first time in North America, this species also characterized by having ciliate bulbs over the upper cortex, but being isidiate, and by the presence of gyrophoric acid in the medulla. Furthermore, B. fungicola and B. tabacina are newly recorded for the state of Oaxaca, B. isidiza for the state of Veracruz, B. subdissecta for the state of Puebla, and B. ventricosa for the states of Morelos and Oaxaca. A thorough revision of Bulbothrix species is proposed, emphasising the correct identification of ciliate bulbs via the diaphanization procedure and the microcrystallization technique for confirming secondary metabolites. A taxonomic key for species of Bulbothrix s. lat. reported in Mexico is provided.

A molecular phylogeny of the genus Sporopodium was inferred from concatenated ITS, mtSSU and nrLSU sequences using maximum likelihood and Bayesian phylogenetic analyses, focusing on material from tropical Asia. A highly supported monophyletic group was recovered as the S. asianum group, characterized by pruinose apothecia or containing epithecial algal cells. Five species belonging to this group are described as new to science from Asia: S. album W. C. Wang & J. C. Wei, with small white apothecia with a loosely farinose margin; S. asianum W. C. Wang & A. Abas, with khaki apothecia, a K+ yellow epithecium and a K+ orange thallus; S. chebalingensis W. C. Wang & J. C. Wei, with a green thallus, bright yellow campylidia, epithecial algal cells and a white apothecial margin; S. flavomarginale W. C. Wang & Ek Sangvichien, with a bluish grey thallus, bright yellow campylidia, pruinose apothecia with epithecial algal cells, and a yellow margin; and S. pruinosum W. C. Wang & J. C. Wei, with a yellowish green thallus, brown campylidia, apothecia with a greyish green disc and a yellow margin. These findings point towards Sporopodium being a genus with a high degree of unrecognized diversity.

We studied the rarely occurring pycnidial conidiomata in three species of the genus Peltigera using electron microscopy (SEM and TEM). Pycnidia are marginal and half-immersed, having unilocular cavities with double-layered walls and slit-shaped ostioles. The conidiophores are composed of sterile basal and very few axial cells, supporting elongated conidiogenous cells. The conidia are produced at their apices by leaving behind phialidic collarettes either at the same level or in a proliferating manner, extending the conidiogenous cells. The study of the ontogeny of the pycnidial conidiomata demonstrates the origin and the gradual development of the characteristic anatomical structures, such as the wall layers, the bursting ostiole, and the non-chambered cavity, which is completely lined by the conidia-forming elements. The combination of these morpho-anatomical details is unique and hence accepted here as ‘Peltigera-type’, in addition to previously recognized pycnidia types (Vobis 1980).

Twenty-five years ago, the dripzone hypothesis, whereby the proximity of understorey conifer branches to the crown of dominant Populus trees significantly increased the diversity and abundance of cyanolichens on these conifers, was first described from western North America. Here, we report a similar phenomenon from eastern North America on conifers under the dripzone of yellow birch and aspen trees. We present field observations of this pattern as well as a quantitative analysis of three humid boreal forests from the Island of Newfoundland. For the latter, we examined epiphytic lichen composition on branches of balsam fir within and immediately outside the dripzone of yellow birch trees. The dripzone effect was strong and spatially restricted to the area under the canopy of yellow birch, as well as aspens, on wet sites in humid forests, with significantly more cyanolichens on balsam fir branches under the yellow birch and aspen canopies. Genera of cyanolichens predominantly found under the dripzone included Fuscopannaria, Leptogium, Lobaria, Lobarina, Neproma, Pannaria, Parmeliella, Pectenia, Pseudocyphellaria and Ricasolia, and included the COSEWIC listed Pectenia plumbea. We suggest here that the canopy of broadleaf phorophytes not only shape the cyanolichen community on understorey conifers by chemical enrichment of the throughfall, but also probably from enrichment by cyanolichens within their own canopy, which also contribute abundant cyanolichen propagules.

Small, isolated populations of cold-adapted species at the edge of their climatic range are highly sensitive to environmental change, making them powerful ecological indicators. Cetraria sepincola (Ehrh.) Ach. is an epiphytic lichen which illustrates this role. It is common in Nordic countries, but in the southern parts of its European range, its distribution has become fragmented and restricted to cold habitats. We studied populations in habitats of high conservation value such as wetlands, montane stone fields, and wooded meadows in south-west Germany, where it persists at the edge of its ecological range in Central Europe and is becoming increasingly rare. Its dependence on specific climatic conditions and selectivity in its photobiont associations make it particularly responsive to shifts in climate and land use. Through historical records, recent observations, data on nitrogen deposition and associated species, we identified key environmental factors shaping the distribution of C. sepincola. Our analysis confirms that populations in south-west Germany occur at the climatic margin of the species’ Central European range. We also found that high-density local populations are linked to low ammonia (NH3) concentrations. Cetraria sepincola associated specifically with Trebouxia lineages from clade S (e.g. OTU S28 = Trebouxia barrenoae and OTU S27), commonly found in lichens from acidic substrates. We found the same Trebouxia lineages in the co-occurring acidophyte Hypogymnia physodes (L.) Nyl., a likely local photobiont donor for C. sepincola, which lacks asexual propagules. At some sites, species of the nitrophytic Xanthorion community started to colonize the same twigs as C. sepincola. In our study area, typically more nitrophytic species from the families Teloschistaceae (e.g. Polycauliona polycarpa (Hoffm.) Frödén et al., Xanthoria parietina (L.) Th. Fr.) and Physciaceae (Physcia adscendens H. Olivier) host Trebouxia algae from clades which are incompatible with C. sepincola. The spread of nitrophytic species and their associated photobionts into formerly acidophytic communities could also reduce the likelihood of finding compatible photobionts for C. sepincola. Climate change, possible direct toxic effects of NH3 on the mycobiont, and indirect impact of NH3 on the lichen and photobiont community exacerbate the extinction risk for sensitive lichens, particularly at the edge of their distribution range.

Nine species and one variety of lichenicolous fungi are reported on Megaspora verrucosa var. verrucosa. Of these, five species and one variety are described as new to science: Arthonia aspiciliae var. megasporae, with black, epruinose, superficial ascomata, a brownish grey, I+ red hymenium, brown, K+ greyish to olivaceous epihymenium and hypothecium, non-capitate paraphysoids lacking a dark apical cap, and hyaline, heteropolar, 1-septate, non-halonate ascospores; Leptosphaeria verrucosae, with epapillate ascomata, well-developed periphysoids and long interascal filaments, 2-spored asci, and olivaceous buff, 3-septate, comparatively large ascospores up to 55 μm long; Merismatium subnigritellum, with ascomata mainly 150–220 μm diam. and (sub)muriform ascospores mainly 14–18 × 8–9.5 μm, showing (6–)8–11(–18) cells in optical section; Polycoccum megasporae, with finally verrucose, 1(–3)-septate, comparatively large ascospores up to 44 μm long; Stigmidium kudratovii, growing on the apothecial discs of the host, with abundant, macroscopically conspicuous, dark vegetative hyphae, pseudoparaphyses of ‘type a’, hyaline, 1-septate, smooth-walled, non-halonate, BCr− ascospores, and lacking paraphysoids; and Talpapellis ochirbatae, with abundant superficial hyphae, relatively short, occasionally branched conidiophores, and (0–)1(–2)-septate conidia in short chains. A presumably undescribed taxon of Lichenostigma subgen. Lichenogramma growing on the same host, with relatively sparse, scarcely ramified plurihyphal vegetative strands, 1–3-septate ascospores, and thalloconidia, is characterized. A key to the 17 species of lichenicolous fungi reported on Megaspora verrucosa is provided.

The new lichenicolous fungus Polycoccum boquerasiae growing on the thallus of corticolous Lecania cyrtella is described and compared with similar species. In addition to the host selection, the species is characterized by comparatively small ascomata, 35–80 μm diam., and narrow ascospores measuring 8–12.5 × 2.5–4.5 μm. A key to all known Polycoccum species is provided.

The population dynamics of the epiphytic lichen Lobaria pulmonaria were studied in spruce forests within Paanajärvi National Park (Karelia), which has seen no major disturbances during the last 190 to 270 years. Studies for the period 2015–2021 showed a rise in thallus number and area, with a larger proportion in the ontogenetic spectrum being young, non-reproductive thalli (virginal 1). Sexual reproduction was low, with fertile thalli comprising less than 1% of the total. Salix caprea and Populus tremula trunks served as the main growth surfaces for Lobaria pulmonaria in the northern taiga forests. Furthermore, Salix caprea offered the optimal environment for thalli to grow and develop. In a few instances, the colonization of new substrata was observed. Climate change is expected to have a positive impact, allowing the species’ range expansion at its northern border.

Lichens have long been recognized as indicator species of environmental health and microclimate stability because they passively regulate their internal water status. Rather, lichens modulate their environment-to-internal water status relationships through structural adaptations in the thallus. Pseudocyphellae, breaks in the upper and lower cortex that expose the medulla, are present across unrelated lineages of lichens. However, they have rarely been studied from a functional physiological perspective in the tropical ecosystem, an ecologically important yet understudied biome. To understand the role of traditionally measured thallus-related traits (thickness, area, specific mass and water holding capacity) and pseudocyphellae-related traits (size and density) in regulating water status, we investigated the tropical lichen Crocodia aurata (Peltigeraceae) at three sites situated along a precipitation gradient in Monteverde, Costa Rica. We hypothesized that drying rate (k) is predicted by differences in water availability along a natural precipitation gradient, and that thallus and pseudocyphellae traits drive variation in k across this gradient. To test this hypothesis, we calculated the drying rate and measured thallus traits in 60 thalli across three sites spanning ~600 m of elevation and differing by 1000–1500 mm in annual precipitation. Consistent with ecophysiological theory, which suggests that lichens in wetter habitats will dry faster to maintain a favourable, intermediate water status, we found that samples of Crocodia aurata from wetter sites dried significantly faster than those from drier sites. All traditionally measured thallus traits predicted drying rate while pseudocyphellae-related traits did not significantly predict drying rate. This suggests that pseudocyphellae may not play a primary role in regulating the drying process in Crocodia aurata, in response to water availability along a tropical precipitation gradient. Instead, traditionally measured thallus traits remain the dominant drivers of drying rates. These findings contribute to our understanding of the acclimation of lichens to different climatic conditions and emphasize the complex interaction between environmental factors and morphological traits. Studying water relations and corresponding functional traits of these poikilohydric organisms is critical if we are to understand how these ecologically important organisms interact with their environments as a function of specific functional traits, and hence understand future impacts of changing climates.

Lichens containing unicellular cyanobionts have received scant attention regarding their nitrogen- (N2-) fixing capacities. Thyrea girardii (Lichinomycetes), containing the putative cyanobiont Chroococcidiopsis, is the only species in this group so far reported to fix N2. Nitrogenase activity in T. girardii was higher in the light than in the dark, counter to overwhelming evidence that free-living unicells fix N2 in the dark only, providing temporal separation from oxygenic photosynthesis in the light. The original focus of the current work was to better understand the strategies by which N2 fixation and photosynthesis might operate concurrently in species of Lichinella (Lichinellaceae) and Thyrea (Porocyphaceae) but this aim was frustrated by the infrequency with which nitrogenase activity was detected in the populations sampled. This problem itself became a principal topic of this report. Lichinella nigritella, Thyrea confusa and T. girardii were collected in Catalonia, Spain and subjected to measurements of nitrogenase activity (acetylene reduction) and net CO2 exchange. Of 91 specimens of the three species combined that were tested, 49 had zero nitrogenase activity and only 23 had activity ≥ 5 nmol C2H4 g−1 h−1 with no obvious trends among species. Nitrogenase activity was consistently greater in the light than in the dark during diel dark-light-dark transitions. Maximum rates of nitrogenase activity recorded for L. nigritella, T. confusa and T. girardii were 133.4, 28.7 and 47.0 nmol C2H4 g−1 h−1, respectively. All specimens tested were photosynthetically competent, although rates of net CO2 exchange were comparatively low (maximum rates in L. nigritella and T. girardii were 37 and 16%, respectively, of maximum rates in Peltigera membranacea), and there was no evidence that photosynthetic rates were lower in thalli with appreciable nitrogenase activity. 15N natural abundance values for L. nigritella and T. girardii (δ15N = −3.41 and −0.84 ‰, respectively) were in agreement with published values for lichens with cyanobacterial photobionts. The results are discussed in relation to possible explanations for the low frequency of nitrogenase activity in these species, its occurrence in the light, and potential confounding factors (the presence of epiphytic heterocytous cyanobacteria and N pollution). It is suggested that the capacity of unicellular cyanobacteria to rapidly switch between non-diazotrophic and diazotrophic states may be advantageous in lichens with unicellular cyanobionts in habitats where N supply is only occasionally limiting.