Population genetics investigates the distribution of genetic variation in natural populations and the genetic differentiation among populations. Lichen-forming fungi are exciting subjects for population genetic studies due to their obligate symbiosis with a green-algal and/or cyanobacterial photobiont, and because their different reproductive strategies could influence fungal genetic structures in various ways. In this review, first, I briefly summarize the results from studies of chemotype variation in populations of lichen-forming fungi. Second, I compare and evaluate the DNA-based molecular tools available for population genetics of lichen-forming fungi. Third, I review the literature available on the genetic structure of lichen fungi to show general trends. I discuss some fascinating examples, and point out directions for future research.

To test the phylogenetic position of phenotypically peculiar species in the Physciaceae we generated 47 new sequences (26 of nrITS region and 21 of mtSSU rDNA) from 19 crustose taxa of Physciaceae mainly from the genus Rinodina. Phylogenetic analysis confirmed the Buellia and Physcia groups. The analysis revealed a considerable variability of characters traditionally used for classification, especially in the delimitation of the genera Buellia and Rinodina. While ascus types agree well with the distinction of the Buellia and Physcia groups, none of the other traditional characters, including excipulum type and ascospore thickening, were consistent within subclades of the Physcia group. We suggest that both excipulum type and ascospore characters are rather dynamic in the evolution of Rinodina species and only appear consistent in morphologically more complex foliose and fruticose groups, which are characterized by thallus characters not present in the crustose groups. Two recent taxonomic changes are supported by molecular characters: Endohyalina insularis (syn. ‘Rinodina’ insularis) and Rinodina lindingeri (syn. ‘Buellia’ lindingeri). In addition Rinodina parvula (syn. ‘Buellia’ parvula) is reinstated. New records for Endohyalina brandii, E. diederichii, E. insularis and Rinodina albana are presented.

Hysterium graphideum Speg. is proposed as a synonym of Gloniella graphidoidea Rehm. During the study of the types of both names, the presence of algae associated with the fungal hyphae was found. The main morphological and anatomical characters, and the ecology of the species are presented.

Two species, Cliostomum coppinsii Fryday & Kantvilas sp. nov. from Scotland, and Cliostomum praepallidum (Müll. Arg.) Kantvilas & Fryday comb. nov. from Tasmania and southern South America, are described, illustrated and discussed. Both occupy an unusual position within the genus on account of their atypically wide, ± polarilocular ascospores. Patellaria banksiae Müll. Arg., based on a collection from Australia, is lectotypified and reduced to synonymy with Cliostomum griffithii (Sm.) Coppins.

Recent revisions of the graphidaceous lichens of India have brought to light several new taxa in the family Graphidaceae. In the present study seven species of Acanthothecis are recognized from India. Three new species, viz. Acanthothecis archeri, A. celata, and A. coccinea, are described and A. nivalis, a species described earlier from the Andaman Islands, has now been recorded from the mainland. A revised key to the seven Acanthothecis species so far known from India is also presented.

The new species, Maronina orientalis Kantvilas & Papong, with two varieties, var. orientalis and var. corallifera Kantvilas & Papong, is described, based on material from Thailand. The genus Maronina, now containing four species, is reassessed. It is characterized by having a crustose thallus, lecanorine apothecia and polysporous asci of a modified Lecanora-type.

Psoroma microlepideum is reduced to a synonym of P. fuegiense. The species differs in several characters from P. pholidotum, and it overlaps geographically with the latter, which is neotypified here. These two species are now placed in the new southern South American genus Psorophorus, differing from Psoroma s. str. in being corticolous, having adpressed squamules on a distinct, dark prothallus, lacking melanins, having a thin cortical layer and a simpler IKI+ apical ascus structure. Two other widespread, panaustral species are the only ones in Pannariacae containing usnic acid. The primarily fertile species has been known as Psoroma pholidotoides, but the type contains pannarin rather than usnic acid, and the correct name for the primarily fertile taxon with usnic acid is Psoroma contextum Stirt. This is together with P. soccatum R. Br. ex Crombie is now placed in the new genus Xanthopsoroma. In addition to usnic acid, both species have a series of distinct terpenoids, some in major quantities. Like Psorophorus, they are corticolous, but have long, more or less nodulose, apical perispore extensions, and an IKI+ apical ascus tube structure which is longer and thinner, including a diffuse tholus reaction, and often an external apical sheet. Phylogenetically, these two genera are shown to be monophyletic and different from Psoroma s. str. based on an analysis of ITS and nrLSU rDNA. This analysis also shows that among the ten species focused on in this study, nine species (two in Xanthopsoroma, two in Psorophorus and five in Psoroma s. str.) are monophyletic, based on two to six sequences of each species. Psoroma hypnorum remains polyphyletic. All names now belonging in Psorophorus and Xanthopsoroma are typified.

The species assigned to the genus Catillochroma are reassessed. The two characters used to characterize Catillochroma, exciple anatomy and thalline chemistry, are shown to be variable and contradictory with a number of intermediates. Consequently, Catillochroma is reduced to synonymy with Megalaria, and the species previously placed in Catillochroma transferred, or returned, to Megalaria. As such, the following new combinations are proposed: Megalaria anaglyptica, M. endochroma, M. intermiscens and M. leptocheila. The genus Lopezaria is also shown to be related to Megalaria and to be closely related to the type species of Catillochroma, C. endochroma, and so is also reduced to synonymy with Megalaria. A number of species found to have been misplaced in Catillaria are also transferred to Megalaria: M. leucochlora, M. melanopotamica, M. obludens, M. pannosa and M. phaeolomiza. Megalaria imshaugii is reduced to synonymy with M. obludens, Megalaria pannosa is reported for the first time from North America and Lopezaria isidiza is reported for the first time from outside Asia from Jamaica.

This paper presents a study to partition the role of three regional-scale drivers – woodland extent and continuity, pollution regime, and climatic setting – in explaining the composition and richness of lichen epiphytes in Scotland. To do this we used partial canonical correspondence analysis and multiple least squares regression, to examine lichen communities across 170 study sites. First, our results demonstrate the importance of climate in explaining species composition. This highlights the relatively clean-air environment of Scotland within a European setting, and emphasizes the important consideration of regional context in the development of bioclimatic species-response models. This result contrasts with a previous similar study which collapsed complex environmental data into summary gradients, and which therefore discounted climate as a key factor. Second, we show a functional decoupling between composition and species richness, which was optimally explained by old-growth woodland extent and pollution, and only weakly explained by climate. The difference in explanatory variables between composition and richness is a focal issue in determining the processes by which species compositional change, driven by rapid and deep climate change, may indirectly impact species richness. For example, this impact may occur through an imbalance in rates of species extinction (for sensitive range-edge species) and establishment in a fragmented landscape (for dispersal-limited colonists), though operating against the ‘stabilizing effect’ of microclimatic setting.

Gastropod abundance was quantified in forest litter around 33 trees harbouring Lobaria pulmonaria in southern Norway. In total, 1709 snails representing 28 species were found, and the number of snail species strongly increased with the total number of specimens found. Number of snail species, as well as snail abundance, was highest around trees on high pH soils. There was a positive relationship between number of snail specimens and cover of grazing traces on L. pulmonaria, presumably because calcareous soils facilitate both litter dwelling and climbing gastropods. The results suggest that gastropods may limit the distribution of L. pulmonaria in calcareous broad-leaved forests.