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.

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.

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.

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.

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.

The genus Canoparmelia Elix & Hale contains c. 40 species, predominantly occurring in tropical and subtropical regions. The genus is characterized by having relatively narrow, subirregular lobes with rotund or subrotund eciliate margins, a pored epicortex, the presence of isolichenan in the cell walls, bifusiform conidia, and simple rhizines (Elix 1993; Crespo et al. 2010b). Phylogenetically, it belongs to the Parmotrema clade of parmelioid lichens (Crespo et al. 2010b). Since its original circumscription (Elix et al. 1986), species have been transferred to other genera, including Austroparmelina A. Crespo et al. (Crespo et al. 2010a), Crespoa (D. Hawksw.) Lendemer & B. P. Hodk. and Parmotrema A. Massal. (Crespo et al. 2010b; Hawksworth 2011; Lendemer & Hodkinson 2012; Kirika et al. 2016). In addition, some species of the genus Crespoa are morphologically similar to certain Canoparmelia species, which leaves uncertainty regarding the identification of the samples.