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Abstract The analysis of the interaction between main bionts (mycobiont and photobiont) in the lichen symbiosis delivers substantial information about their preferences in the selection of symbiotic partners, and their ecological preferences. The selectivity in the Parmelia genus has been defined as strong so far. However, data on this lichen genus, which includes several widely distributed species, are biogeographically limited. Therefore, using specialization indicators and extended sampling, in this study, we estimated the interactions between the main bionts of selected Parmelia spp., using two levels of estimation (species/OTU and haplotype). A comparison of mycobiont-photobiont interactions at different levels showed that considering only mycobiont species and Trebouxia OTUs, greater specialization is found, while Parmelia species studied in this work present a more generalistic strategy in photobiont choice when haplotypes are considered. Despite the uneven sampling of Parmelia species, the interpretation of specialization within species and individuals of the genus leads to a more precise and accurate interpretation of their adaptation strategies. Furthermore, the data from P. sulcata indicate the existence of a different pool of compatible haplotypes in some geographical regions compared to neighboring areas. This observation suggests the potential influence of climatic factors.

The analysis of the interaction between main bionts (mycobiont and photobiont) in the lichen symbiosis delivers substantial information about their preferences in the selection of symbiotic partners, and their ecological preferences. The selectivity in the Parmelia genus has been defined as strong so far. However, data on this lichen genus, which includes several widely distributed species, are biogeographically limited. Therefore, using specialization indicators and extended sampling, in this study, we estimated the interactions between the main bionts of selected Parmelia spp., using two levels of estimation (species/OTU and haplotype). A comparison of mycobiont-photobiont interactions at different levels showed that considering only mycobiont species and Trebouxia OTUs, greater specialization is found, while Parmelia species studied in this work present a more generalistic strategy in photobiont choice when haplotypes are considered. Despite the uneven sampling of Parmelia species, the interpretation of specialization within species and individuals of the genus leads to a more precise and accurate interpretation of their adaptation strategies. Furthermore, the data from P. sulcata indicate the existence of a different pool of compatible haplotypes in some geographical regions compared to neighboring areas. This observation suggests the potential influence of climatic factors. [ABSTRACT FROM AUTHOR]

The effect of dust pollution on the photosynthesis and respiration parameters of foliose lichens Hypogimnia physodes (L.) Nyl, Lobaria pulmonaria (L.) Hoffm. and Peltigera aphthosa (L.) Willd., collected near the bauxite mine (Komi Republic, Russia) was investigated. Microscopic analysis showed that fine dust particles were mainly on the thalli surface, with a few mineral inclusions in the thalli medulla. The deposition of dust particles caused significant changes in the optical properties of the lichen surface in the visible and infrared spectral regions. A number of spectral indices (BRI, REP, RES, WI) sensitive to lichen pollution by dust emissions from the bauxite mine were identified due changes in the reflectance spectra of the thalli. Shading of the algal layer by mineral particles deposited on the thalli surface did not affect the content of photosynthetic pigments and PS II photochemical activity parameters. At the same time, lichen CO2-exchange parameters were observed to change. Lichen thalli from the polluted area were characterized by lower values of net CO2 uptake in the moderate light conditions (150 µmol PAR/m2 s), and the proportion of dark respiration in the gas exchange was 1.5 to 2 times higher than the values for thalli from background site. A 2-fold decrease in cytochrome respiration capacity was observed in thalli from the affected area. In thalli of L. pulmonaria and P. aphthosa, the energetically inefficient alternative respiratory pathway capacity increased 1.5‑fold and in H. physodes the activity of residual respiration increased more than 3.5-fold. The results obtained allowed an assessment of the chronic dust pollution effects on the foliose lichens symbionts functioning. The data may be useful for environmental biomonitoring. [ABSTRACT FROM AUTHOR]

This study investigates the phylogeny and symbiotic relationships of the foliose lichen genus Remototrachyna, R. crenata and R. rhabdiformis from the Western Ghats through morphological, chemical and molecular phylogenetic tools using concatenated ITS and LSU data analyses. The study further identified the photobiont Trebouxia species in R. crenata and R. rhabdiformis based on ITS sequence data and phylogeny. The Trebouxia species of R. crenata and R. rhabdiformis were delineated as a major clade closely related to Trebouxia sp. voucher SF31 sequenced from Usnea ghattensis belonging to Trebouxia Clade I. This study represents a pioneering effort to unravel the enigmatic lichen symbiosis that exists in the genus Remototrachyna from the Western Ghats of India. [ABSTRACT FROM AUTHOR]

Cyanobacteria require liquid water for photosynthesis, whereas green algae can photosynthesise with water vapour alone. We discovered that several Lobaria spp. which normally have cyanobacteria as the sole photobiont, in some regions of the trans-Himalayas also harboured green algae. We tested whether green algal acquisition was: limited to high elevations; obtained from neighbouring chloro- Lobaria species; enabled photosynthesis at low humidity. Lobaria spp. were collected from 2000 to 4000 m elevation. Spectrophotometry quantified green algal abundance by measuring chlorophyll b (absent in cyanobacteria). Thalli cross-sections visually confirmed green algal presence. We sequenced gene regions: Lobaria (ITS-EF-1α-RPB2), green algae (18S-RBC-L) and Nostoc (16S). Phylogenetic analysis determined myco-photobiont associations. We used a custom closed-circuit gas exchange system with an infrared gas analyser to measure CO2 exchange rates for desiccated specimens at 33%, 76%, 86% and 98% humidity. Cross-sections revealed that the photobiont layers in putative cyano -Lobaria contained both cyanobacteria and green algae, indicating that they should be considered chloro-cyanolichens. Chloro- Lobaria had no visible cephalodia nor cyanobacteria in the photobiont layer. Chloro- Lobaria and chloro-cyano- Lobaria had comparable levels of chlorophyll b. Chloro- Lobaria usually contained Symbiochloris. Chloro-cyano- Lobaria mainly associated with Parachloroidium and Nostoc ; infrequently with Symbiochloris , Apatococcus, Chloroidium , Pseudochlorella, Trebouxia. Sequences from two green algal genera were obtained from within some thalli. Desiccated specimens of every Lobaria species could attain net photosynthesis with light exposure and 33% humidity. CO2 exchange dynamics over a five-day period differed between species. At all elevations, chloro-cyano- Lobaria spp. had abundant green algae in the photobiont layer, but green algal strains mostly differed to those of chloro- Lobaria spp. Both chloro- Lobaria and chloro-cyano- Lobaria were capable of conducting photosynthesis without liquid water. The data strongly suggest that they attained positive net photosynthesis. [ABSTRACT FROM AUTHOR]

While the diversity of foliicolous lichen-forming fungi has been explored in substantial depth, relatively little attention has been paid to their algal symbionts. We studied the unicellular green phycobionts of the lecanoralean lichens Bacidina (Ramalinaceae), Byssoloma , Fellhanera and Tapellaria (Pilocarpaceae) and graphidalean Gyalectidium (Gomphillaceae) from two extratropical foliicolous communities in continental Spain and the Canary Islands. We examined the pyrenoids of algal symbionts within thalli using TEM, and obtained several algal nrSSU and rbcL sequences from whole thalli, and also from cultures isolated from some of these lichens. Pyrenoid structure and molecular sequence data provided support for recognizing Chloroidium (Watanabeales , Trebouxiophyceae) as phycobiont in thalli of Byssoloma subdiscordans and Fellhanera bouteillei (Pilocarpaceae) in both communities. Bacidina apiahica (Ramalinaceae) and Tapellaria epiphylla (Pilocarpaceae) likewise appeared to partner with Chloroidium based on the presence of the same pyrenoid type, although we were able to obtain a phycobiont sequence only from a culture isolate of the latter. These results contrast with those obtained previously from a foliicolous lichen community in southern Florida, which revealed only strains of Heveochlorella (Jaagichlorella) as phycobiont of foliicolous Pilocarpaceae and Gomphillaceae. On the other hand, the pyrenoid we observed in the phycobionts associated with Gyalectidium setiferum and G. minus corresponded to that of Heveochlorella (Jaagichlorella). However, the poor quality of the phycobiont sequence data obtained from G. minus , probably due to the presence of epibiontic algae, could not provide additional perspective on the pyrenoid structure observations. Nonetheless, clear differences in pyrenoid ultrastructure can allow Chloroidium and Heveochlorella phycobionts to be distinguished from each other in TEM. Our results indicate a greater diversity of unicellular green-algal symbionts in foliicolous communities from Spain than previously observed in other geographical areas, and suggest that further studies focused on symbiont pairing in these communities might reveal distinctive and varied patterns of phycobiont preference. [ABSTRACT FROM AUTHOR]

The reproduction and dispersal strategies of lichens play a major role in shaping their population structure and photobiont diversity. Sexual reproduction, which is common, leads to high lichen genetic diversity and low photobiont selectivity. However, the lichen genus Endocarpon adopts a special co-dispersal model in which algal cells from the photobiont and ascospores from the mycobiont are released together into the environment. To explore the dispersal strategy impact on population structures, a total of 62 Endocarpon individuals and 12 related Verrucariaceae genera individuals, representing co-dispersal strategy and conventional independent dispersal mode were studied. Phylogenetic analysis revealed that Endocarpon, with a large-scale geographical distribution, showed an extremely high specificity of symbiotic associations with their photobiont. Furthermore, three types of group I intron at 1769 site have been found in most Endocarpon mycobionts, which showed a high variety of group I intron in the same insertion site even in the same species collected from one location. This study suggested that the ascospore-alga co-dispersal mode of Endocarpon resulted in this unusual mycobiont-photobiont relationship; also provided an evidence for the horizontal transfer of group I intron that may suggest the origin of the complexity and diversity of lichen symbiotic associations. [ABSTRACT FROM AUTHOR]

This paper, with Italy as a case-study, provides a general overview on the ecology of lichenicolous lichens, i.e. those which start their life-cycle on the thallus of other lichens. It aims at testing whether some ecological factors do exert a positive selective pressure on the lichenicolous lifestyle. The incidence of some biological traits (photobionts, growth-forms and reproductive strategies) in lichenicolous and non-lichenicolous lichens was compared, on a set of 3005 infrageneric taxa potentially occurring in Italy, 189 of which are lichenicolous. Lichenicolous lichens have a much higher incidence of coccoid (non-trentepohlioid) green algae, crustose growth-forms and sexual reproduction. A matrix of the 2762 species with phycobionts and some main ecological descriptors was subjected to ordination. Lichenicolous lichens occupy a well-defined portion of the ecological space, tending to grow on rocks in dry, well-lit habitats where a germinating spore is likely to have a short life-span, at all altitudes. This corroborates the hypothesis that at least some of them are not true "parasites", as they are often called, but gather the photobionts - which have already adapted to local ecological conditions - from their hosts, eventually developing an independent thallus. [ABSTRACT FROM AUTHOR]

We present a synopsis of studies reporting the free-living occurrence of green algal lichen symbionts. We give an overview of all known lichen photobiont genera together with comprehensive descriptions, taxonomical classification and occurrence data. Based on the analysis of 310 records, we discovered that at least 80% of lichen photobiont genera were observed in the free-living state. Diplosphaera chodatii, Elliptochloris bilobata and Chloroidium ellipsoideum represent both morphologically and genetically the most frequently reported free-living photobiont species. Trebouxia, the most prevalent genus of lichen photobionts, has frequently been reported to exist independently to fungal hyphae. Based on our literature survey, free-living photobionts of lichens are able to grow in a wide range of environments and substrates, with most records coming from soil and biological soil crusts. [ABSTRACT FROM AUTHOR]

Most epiphytic lichens demonstrate high specificity to a habitat type, and sensitive hygrophilous species usually find shelter only in close-to-natural forest complexes. Some of them are considered as old-growth forest and/or long ecological continuity indicators. To evaluate general links between the narrow ecological range and physiological traits, two distinct sets of model lichens, i.e., old-growth forest (Cetrelia cetrarioides (Duby) W.L. Culb. & C.F. Culb., Lobaria pulmonaria (L.) Hoffm., Menegazzia terebrata (Hoffm.) A. Massal.), and generalist (Flavoparmelia caperata (L.) Hale, Hypogymnia physodes (L.) Nyl., Parmelia sulcata Taylor) ones, were examined in terms of sensitivity to long-term desiccation stress (1-, 2-, and 3-month) and photosynthesis activation rate upon rehydration. Desiccation tolerance and response rate to rehydration are specific to a given ecological set of lichens rather than to a particular species. Noticeable delayed and prompt recovery of high photosynthetic activity of photosystem II (PSII) characterize these sets, respectively. At the same time, although a decrease in the potential quantum yield of PSII in lichen thalli with a relative water content (RWC) at the level of 25% was observed, the efficiency remained at a very high level for all species, regardless of habitat preferences. Among the examined lichens, the fluorescence emission parameters for F. caperata were the fastest toward equilibrium upon rehydration, both after a shorter and a longer period of desiccation stress. In contrast to generalist lichens, retrieving of photosynthesis after 3-month desiccation failed in old-growth forest lichens. In the long term, prolonged rainless periods and unfavorable water balance in the environment predicted in the future may have a severely limiting effect on hygrophilous lichens during growing season (also in the sense of species associations) and, at the same time, promote the development of generalists. [ABSTRACT FROM AUTHOR]

Holobionts are dynamic ecosystems that may respond to abiotic drivers with compositional changes. Uncovering elevational diversity patterns within these microecosystems can further our understanding of community‐environment interactions. Here, we assess how the major components of lichen holobionts—fungal hosts, green algal symbionts, and the bacterial community—collectively respond to an elevational gradient. We analyse populations of two lichen symbioses, Umbilicaria pustulata and U. hispanica, along an elevational gradient spanning 2100 altitudinal metres and covering three major biomes. Our study shows (i) discontinuous genomic variation in fungal hosts with one abrupt genomic differentiation within each of the two host species, (ii) altitudinally structured bacterial communities with pronounced turnover within and between hosts, and (iii) altitude‐specific presence of algal symbionts. Alpha diversity of bacterial communities decreased with increasing elevation. A marked turnover in holobiont diversity occurred across two altitudinal belts: at 11°C–13°C average annual temperature (here: 800–1200 m a.s.l.), and at 7°C–9°C average annual temperature (here: 1500–1800 m a.s.l.). The two observed zones mark a clustering of distribution limits and community shifts. The three ensuing altitudinal classes, that is, the most frequent combinations of species in holobionts, approximately correspond to the Mediterranean, cool‐temperate, and alpine climate zones. We conclude that multitrophic microecosystems, such as lichen holobionts, respond with concerted compositional changes to climatic factors that also structure communities of macroorganisms, for example, vascular plants. [ABSTRACT FROM AUTHOR]

The article discusses the current proposals to redefine lichens and highlights the disadvantages of these proposals. Lichens are currently defined as a symbiotic relationship between a fungus (mycobiont) and an alga or cyanobacterium (photobiont). However, some lichen biologists have suggested expanding this definition to include other microorganisms that colonize the lichen thallus. The article argues that these proposals are not justified because the roles and significance of these additional microorganisms are still poorly understood and their inclusion would blur the distinction between lichens and other ecosystems. The article concludes that the current definition of lichens as a partnership between mycobiont and photobiont remains meaningful and should not be amended. [Extracted from the article]

Epiphytic lichens constitute an important component of biodiversity in both deforested and forest ecosystems. Widespread occurrence is the domain of generalist lichens or those that prefer open areas. While, many stenoecious lichens find shelter only in a shaded interior of forests. Light is one of the factors known to be responsible for lichen distribution. Nevertheless, the effect of light intensity on photosynthesis of lichen photobionts remain largely unknown. We investigated photosynthesis in lichens with different ecological properties in relation to light as the only parameter modified during the experiments. The aim was to find links between this parameter and habitat requirements of a given lichen. We applied the methods based on a saturating light pulse and modulated light to perform comprehensive analyses of fast and slow chlorophyll fluorescence transient (OJIP and PSMT) combined with quenching analysis. We also examined the rate of CO2 assimilation. Common or generalist lichens, i.e. Hypogymnia physodes, Flavoparmelia caperata and Parmelia sulcata, are able to adapt to a wide range of light intensity. Moreover, the latter species, which prefers open areas, dissipates the excess energy most efficiently. Conversely, Cetrelia cetrarioides considered an old-growth forest indicator, demonstrates definitely lower range of energy dissipation than other species, although it assimilates CO2 efficiently both at low and high light. We conclude that functional plasticity of the thylakoid membranes of photobionts largely determines the dispersal abilities of lichens and light intensity is one of the most important factors determining the specificity of a species to a given habitat. [ABSTRACT FROM AUTHOR]

Carbon‐concentrating mechanisms (CCMs) are a widespread phenomenon in photosynthetic organisms. In vascular plants, the evolution of CCMs ([C44‐carbon compound] and crassulacean acid metabolism [CAM]) is associated with significant shifts, most often to hot, dry and bright, or aquatic environments. If and how CCMs drive distributions of other terrestrial photosynthetic organisms, remains little studied. Lichens are ecologically important obligate symbioses between fungi and photosynthetic organisms. The primary photosynthetic partner in these symbioses can include CCM‐presenting cyanobacteria (as carboxysomes), CCM‐presenting green algae (as pyrenoids) or green algae lacking any CCM. We use an extensive dataset of lichen communities from eastern North America, spanning a wide climatic range, to test the importance of CCMs as predictors of lichen ecology and distribution. We show that the presence or absence of CCMs leads to opposite responses to temperature and precipitation in green algal lichens, and different responses in cyanobacterial lichens. These responses contrast with our understanding of lichen physiology, whereby CCMs mitigate carbon limitation by water saturation at the cost of efficient use of vapor hydration. This study demonstrates that CCM status is a key functional trait in obligate lichen symbioses, equivalent in importance to its role in vascular plants, and central for studying present and future climate responses. [ABSTRACT FROM AUTHOR]

Lichenized fungi as a multicomponent biological system are an interesting but difficult research object. In view of the complex interaction of the myco- and photobiont, the slow growth of natural thalli, their exceptional exactingness to environmental factors, the study of the biological characteristics of lichens is significantly difficult. This article discusses the problem of studying the anatomical and morphological structure of the myco- and photobiont of lichenized fungi using the tissue culture method on the example of rare species (Lobaria pulmonaria) and species with pharmaceutical potential (Usnea dasopoga, Cetraria islandica). The authors proposed a method for cultivating of myco- and photobionts of these species on synthetic nutrient media for the purpose of further research on the characteristics of lichenized fungi. Fragments of thalli, apothecia (for C. islandica), and soredia (for U. dasopoga and L. pulmonaria) were used as donor material. For the introduction of the photobiont under sterile conditions, a homogenate of the thallus region was prepared. Pure cultures of the myco- and photobiont of L. pulmonaria, U. dasopoga, and C. islandica were obtained on three types of hormone-free nutrient media, namely MS nutrient medium, modified MS medium with a reduced nitrogen content, Czapek medium. The verification of the research results was carried out taking into account the microscopy of the obtained cultures of myco- and photobionts. Using microscopy, the dimensional characteristics of the obtained mycobionts were determined. The diameters of the hyphae of L. pulmonaria, U. dasopoga, and C. islandica were 4.3–4.4 µm, 4.6 µm, and 4.1–4.3 µm, respectively, which corresponds to the size of the hyphae in natural samples. The use of the tissue culture method makes it possible to study and analyze the biological characteristics of lichenized fungi as a multicomponent biological system, as well as to contribute to the preservation of rare species and their components in the Red Data Book; while optimizing the method of cultivating myco- and photobiont on synthetic nutrient media, to reduce the anthropogenic load on natural populations of lichens when using them as medicinal raw materials.

Lichens have long been considered as composite organisms composed of algae and/or cyanobacteria hosted by a fungus in a mutualistic relationship. Other organisms have been gradually discovered within the lichen thalli, such as multiple algal species, yeasts, or even viruses. Of pivotal relevance is the existence of the lichen microbiome, which is a community of microorganisms that can be found living together on the lichen surface. This community performs a growing number of functions. In this entry, we explore the journey of lichens being considered from a dual partnership to a multi-species symbiotic relationship.

Gyalectidium setiferum Vězda & Sérus., a foliicolous lichen characterized by having some vertically oriented whitish translucent cilia surrounding a swollen greenish diahyphal mass, is reported as new to East Asia. It was collected from two localities on the lowlands of central Honshu in Japan where it grew on leaves of Aucuba japonica and Maesa japonica. The description with illustration based on the Japanese material is given. Gyalectidium setiferum has been included in this genus due to its morphological features even though no fertile specimen has been found so far. The monophyly of this species and its position in this genus were newly confirmed by the molecular phylogenetic analysis based on mtSSU and nrLSU. [ABSTRACT FROM AUTHOR]

The heavy metal Cd accumulates in trophic chains, constituting a toxic element for photosynthesizing organisms, including the algal photobionts of lichen. Thus, as lichens respond differently to heavy metal toxicity, we hypothesized that the species Parmotrema tinctorum and Usnea barbata, commonly sampled in the Cerrado ecoregion, could be sensitive to Cd and, therefore, be used to biomonitor the dispersion of this metal. We also aimed to indicate the responsiveness of biological markers to Cd in these species by exposing the thalli to simulated rainfall with increasing metal concentrations. We observed that both lichen species are responsive to Cd stress; however, different pathways are accessed. The synthesis of carotenoids by P. tinctorum and the production of antioxidant enzymes by U. barbata seem to constitute relevant response strategies to Cd-induced stress. The lichen morphoanatomy, cell viability, photobiont vitality index, chlorophyll a fluorescence, and chlorophyll a synthesis were efficient biomarkers for the effects of increasing Cd exposure in P. tinctorum, being the variables primarily associated with damage to the photobiont. For U. barbata, the lichen morphoanatomy, photochemistry, and antioxidant enzyme activity (catalase, superoxide dismutase and ascorbate peroxidase) were essential to reflect Cd toxicity. However, the species P. tinctorum was characterized as the most sensitive to Cd toxicity, constituting a good bioindicator for the presence of this metal. It can be used in the diagnosis of air quality in urban and industrial areas or even in forest areas influenced by Cd in phosphate fertilizers. [ABSTRACT FROM AUTHOR]

Definition: Lichens have long been considered as composite organisms composed of algae and/or cyanobacteria hosted by a fungus in a mutualistic relationship. Other organisms have been gradually discovered within the lichen thalli, such as multiple algal species, yeasts, or even viruses. Of pivotal relevance is the existence of the lichen microbiome, which is a community of microorganisms that can be found living together on the lichen surface. This community performs a growing number of functions. In this entry, we explore the journey of lichens being considered from a dual partnership to a multi-species symbiotic relationship. [ABSTRACT FROM AUTHOR]

Trentepohliales are a group of both free‐living and lichenized algae, with most diversity occurring in tropical regions. Recent studies showed that the abundance of lichens with a trentepohlioid photobiont has been increasing in temperate habitats, probably because of global warming, which makes them an interesting study case. A detailed molecular study of the diversity of lichenized Trentepohliales, epiphytic as well as epilithic, was performed in three forests of north‐western Europe. Additional samples of lichens of the Arthoniales order (associating essentially with a trentepohlioid photobiont) from other European regions and from other continents were also sequenced. A total of 195 algal sequences were obtained. Phylogenetic analyses with rbcL and ITS loci were performed and associations between phylogenetic distances of photobionts and ecological factors (substratum, climate or Wirth indices, mycobiont taxonomy, and geographic location) were tested by variation partitioning and phylogenetic signal analyses. The high number of rbcL algal haplotypes found in some lichens or on different substrata revealed that the Trentepohliales diversity in extratropical regions was underestimated. The phylogenetic patterns showed selectivity of some photobionts in their fungal partner choice and vice‐versa, while others were linked with several haplotypes. Photobionts seemed to be less selective than mycobionts. The main factors influencing lichenized algal community were climate and mycobiont species. Coevolution between mycobionts and photobionts as well as switching between free living and lichenized lifestyles appeared to drive the evolution of Trentepohliales and might explain the high cryptic diversity observed, which might be changing in some regions due to climate change. [ABSTRACT FROM AUTHOR]

Coccoid microalgae of the genus Trebouxia Puymaly are by far the most prevalent among the various species involved in lichen symbioses. However, their taxonomic knowledge is rather scarce compared to that of lichenized fungi. In the present work, a taxonomic study integrating diverse techniques (phylogenetics, light, confocal and transmission electron microscopies) is carried out to describe Trebouxia maresiae Garrido-Benavent, Chiva & Barreno, sp. nov. This species widely associates with the red-listed lichenized fungus Seirophora villosa (Ach.) Frödén but also with species of the genus Ramalina Ach., both occurring in coastal environments in the western Mediterranean and the Cape Verdean islands. This microalga is circumscribed to Trebouxia clade A and is closely related to T. de colorans Ahmadjian. It is characterized by the cell size being up to 15 µm in diam., the crenulate chloroplasts, and the structure of pyrenoids, which in cultured cells fits well with the crenulata-type, with long branched tubules meandering through the pyrenoid matrix, whereas in the lichenized state it acquires a hybrid structure (maresiae-type), characterized by the periphery of the pyrenoid being rather gigantea-type, with thylakoid membranes forming short, branched tubules. With the present work, the taxonomy of the genus Trebouxia moves a step forward towards more accurately characterizing species in lichen microalgae which is a prerequisite for future, more complex studies on speciation, co-evolution and selectivity. [ABSTRACT FROM AUTHOR]

Water use traits in lichens are important attributes that determine the duration of hydration and metabolically active periods. In this study, the water holding capacity (WHC) and specific thallus mass (STM) were measured for seven macrolichen species (Parmelia sulcata , Parmelina tiliacea , Evernia prunastri , Ramalina farinacea , Lobaria pulmonaria , Lobarina scrobiculata and Nephroma resupinatum) from a Temperate-Mediterranean fragmented landscape. Twenty Quercus forests with different environmental conditions were selected to gather therein five lichen samples of each species in order to analyse their interspecific and intraspecific variation in WHC and STM. The type of photobiont was mainly responsible for differences in the WHC and the water content per biomass among species. Lichens with cyanobacteria as the main or secondary photobiont showed the highest value for both parameters. However, particular features of species were more important in modulating STM, while growth form had a minor explanatory importance. At the intraspecific level, variation in WHC relied on climatic, microclimatic and forest structure factors, while STM variability was only dependent on the two last predictors. Future research should be focused on other drivers at the microscale to unveil the environmental conditions that shape WHC and STM in lichens. • The type of photobiont primarily shapes water holding capacity in macrolichens. • Specific thallus mass in macrolichens depends on particular features of species. • Growth forms are not so relevant to explain interspecific variability in macrolichens. • The water content per biomass relies on the type of photobiont. • Intraspecifically, water use traits primarily respond to microscale factors. [ABSTRACT FROM AUTHOR]

We propose that a qualitative trait approach based on more detailed nuanced traits may reveal previously overlooked patterns, especially when combined with phylogenetic perspectives. By sampling epiphytic lichens and using a functional approach based on nuanced qualitative traits, such as a much greater resolution over photobiont identity, type of cortex, and chemical compounds, we evaluated the effects of environmental filtering and phylogenetic constraints on community assembly along a natural succession of Atlantic rainforest. We found changes in taxonomic, functional, and phylogenetic composition, structure, and diversity. Functional traits such as photobiont genera, type of cortex, reproductive structures, propagule size, and protection strategies showed strong responses to succession. Mature forests with a closed canopy impose strong environment filtering that is reflected in lichen species turnover, limiting diversity, but also holding different functional and phylogenetic composition. The use of a nuanced qualitative trait approach may overcome some of the limitations of using this type of traits and shows the importance of often‐overlooked key lichen functional traits, including the presence of carbon‐concentrating mechanisms in photobionts and cortex properties. Furthermore, this is the first study showing how patterns of phylogenetic assembly along forest succession structure lichen communities. [ABSTRACT FROM AUTHOR]

Lichen associations are overwhelmingly supported by carbon produced by photosynthetic algal symbionts. These algae have diversified to occupy nearly all climates and continents; however, we have a limited understanding of how their climatic niches have evolved through time. Here we extend previous work and ask whether phylogenetic signal in, and the evolution of, climatic niche, varies across climatic variables, phylogenetic scales, and among algal lineages in Trebouxia— the most common genus of lichen-forming algae. Our analyses reveal heterogeneous levels of phylogenetic signal across variables, and that contrasting models of evolution underlie the evolution of climatic niche divergence. Together these analyses demonstrate the variable processes responsible for shaping climatic tolerance in Trebouxia , and provide a framework within which to better understand potential responses to climate change-associated perturbations. Such predictions reveal a disturbing trend in which the pace at which modern climate change is proceeding will vastly exceed the rate at which Trebouxia climatic niches have previously evolved. [ABSTRACT FROM AUTHOR]

Lichenized algae and cyanobacteria are known to be shared and selected by unrelated lichen-forming fungi coexisting in so-called photobiont-mediated guilds. Life in such a guild could be crucial for the survival of a large group of lichen fungi dependent on horizontal transmission of photobionts. Here, we investigate frequent lichen phycobionts of the genus Trebouxia in rock-dwelling lichen communities. We found intensive and repeated sharing of specific Trebouxia assemblages by co-occurring lichens across distant localities. Rock chemistry, expressed as pH, determined the composition of photobiont pools and separated three saxicolous lichen guilds, sharing environmentally specific photobiont groups. Moreover, unlike the majority of lichen fungi, many Trebouxia photobionts represented opportunists in the choice of general substrate form (soil-rock-tree bark/wood), maintaining their pH preferences. Thus, saxicolous communities form just a part of a complex guild system that is in principle mediated by environmentally conditioned groups of naturally co-occurring photobionts. The complexity of the system is influenced by diverse photobiont life strategies, including also dispersal style. The findings of photobionts strictly or predominantly associated with sexually reproducing fungi stimulated us to emphasize the role of free-dispersing photobionts in the establishment and maintenance of lichen guilds. [ABSTRACT FROM AUTHOR]

Abstract We propose that a qualitative trait approach based on more detailed nuanced traits may reveal previously overlooked patterns, especially when combined with phylogenetic perspectives. By sampling epiphytic lichens and using a functional approach based on nuanced qualitative traits, such as a much greater resolution over photobiont identity, type of cortex, and chemical compounds, we evaluated the effects of environmental filtering and phylogenetic constraints on community assembly along a natural succession of Atlantic rainforest. We found changes in taxonomic, functional, and phylogenetic composition, structure, and diversity. Functional traits such as photobiont genera, type of cortex, reproductive structures, propagule size, and protection strategies showed strong responses to succession. Mature forests with a closed canopy impose strong environment filtering that is reflected in lichen species turnover, limiting diversity, but also holding different functional and phylogenetic composition. The use of a nuanced qualitative trait approach may overcome some of the limitations of using this type of traits and shows the importance of often‐overlooked key lichen functional traits, including the presence of carbon‐concentrating mechanisms in photobionts and cortex properties. Furthermore, this is the first study showing how patterns of phylogenetic assembly along forest succession structure lichen communities.

Lichen associations are overwhelmingly supported by carbon produced by photosynthetic algal symbionts. These algae have diversified to occupy nearly all climates and continents; however, we have a limited understanding of how their climatic niches have evolved through time. Here we extend previous work and ask whether phylogenetic signal in, and the evolution of, climatic niche, varies across climatic variables, phylogenetic scales, and among algal lineages in Trebouxia—the most common genus of lichen-forming algae. Our analyses reveal heterogeneous levels of phylogenetic signal across variables, and that contrasting models of evolution underlie the evolution of climatic niche divergence. Together these analyses demonstrate the variable processes responsible for shaping climatic tolerance in Trebouxia, and provide a framework within which to better understand potential responses to climate change-associated perturbations. Such predictions reveal a disturbing trend in which the pace at which modern climate change is proceeding will vastly exceed the rate at which Trebouxia climatic niches have previously evolved.

Climatic factors, soil chemistry and geography are considered as major factors affecting lichen distribution and diversity. To determine how these factors limit or support the associations between the symbiotic partners, we revise the lichen symbiosis as a network of relationships here. More than one thousand thalli of terricolous Cladonia lichens were collected at sites with a wide range of soil chemical properties from seven biogeographical regions of Europe. A total of 18 OTUs of the algal genus Asterochloris and 181 OTUs of Cladonia mycobiont were identified. We displayed all realized pairwise mycobiont–photobiont relationships and performed modularity analysis. It revealed four virtually separated modules of cooperating OTUs. The modules differed in mean annual temperature, isothermality, precipitation, evapotranspiration, soil pH, nitrogen, and carbon contents. Photobiont switching was strictly limited to algae from one module, i.e., algae of similar ecological preferences, and only few mycobionts were able to cooperate with photobionts from different modules. Thus, Cladonia mycobionts generally cannot widen their ecological niches through photobiont switching. The modules also differed in the functional traits of the mycobionts, e.g., sexual reproduction rate, presence of soredia, and thallus type. These traits may represent adaptations to the environmental conditions that drive the differentiation of the modules. In conclusion, the promiscuity in Cladonia mycobionts is strictly limited by climatic factors and soil chemistry.

Climatic factors, soil chemistry and geography are considered as major factors affecting lichen distribution and diversity. To determine how these factors limit or support the associations between the symbiotic partners, we revise the lichen symbiosis as a network of relationships here. More than one thousand thalli of terricolous Cladonia lichens were collected at sites with a wide range of soil chemical properties from seven biogeographical regions of Europe. A total of 18 OTUs of the algal genus Asterochloris and 181 OTUs of Cladonia mycobiont were identified. We displayed all realized pairwise mycobiont–photobiont relationships and performed modularity analysis. It revealed four virtually separated modules of cooperating OTUs. The modules differed in mean annual temperature, isothermality, precipitation, evapotranspiration, soil pH, nitrogen, and carbon contents. Photobiont switching was strictly limited to algae from one module, i.e., algae of similar ecological preferences, and only few mycobionts were able to cooperate with photobionts from different modules. Thus, Cladonia mycobionts generally cannot widen their ecological niches through photobiont switching. The modules also differed in the functional traits of the mycobionts, e.g., sexual reproduction rate, presence of soredia, and thallus type. These traits may represent adaptations to the environmental conditions that drive the differentiation of the modules. In conclusion, the promiscuity in Cladonia mycobionts is strictly limited by climatic factors and soil chemistry. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

The heavy metal Cd accumulates in trophic chains, constituting a toxic element for photosynthesizing organisms, including the algal photobionts of lichen. Thus, as lichens respond differently to heavy metal toxicity, we hypothesized that the species Parmotrema tinctorum and Usnea barbata, commonly sampled in the Cerrado ecoregion, could be sensitive to Cd and, therefore, be used to biomonitor the dispersion of this metal. We also aimed to indicate the responsiveness of biological markers to Cd in these species by exposing the thalli to simulated rainfall with increasing metal concentrations. We observed that both lichen species are responsive to Cd stress; however, different pathways are accessed. The synthesis of carotenoids by P. tinctorum and the production of antioxidant enzymes by U. barbata seem to constitute relevant response strategies to Cd-induced stress. The lichen morphoanatomy, cell viability, photobiont vitality index, chlorophyll a fluorescence, and chlorophyll a synthesis were efficient biomarkers for the effects of increasing Cd exposure in P. tinctorum, being the variables primarily associated with damage to the photobiont. For U. barbata, the lichen morphoanatomy, photochemistry, and antioxidant enzyme activity (catalase, superoxide dismutase and ascorbate peroxidase) were essential to reflect Cd toxicity. However, the species P. tinctorum was characterized as the most sensitive to Cd toxicity, constituting a good bioindicator for the presence of this metal. It can be used in the diagnosis of air quality in urban and industrial areas or even in forest areas influenced by Cd in phosphate fertilizers.

Interactions within lichen communities include, in addition to close mutualistic associations between the main partners of specific lichen symbioses, also more elusive relationships between members of a wider symbiotic community. Here, we analyze association patterns of cyanolichen symbionts in the tropical montane forests of Taita Hills, southern Kenya, which is part of the Eastern Afromontane biodiversity hotspot. The cyanolichen specimens analyzed represent 74 mycobiont taxa within the order Peltigerales (Ascomycota), associating with 115 different variants of the photobionts genus Nostoc (Cyanobacteria). Our analysis demonstrates wide sharing of photobionts and reveals the presence of several photobiont-mediated lichen guilds. Over half of all mycobionts share photobionts with other fungal species, often from different genera or even families, while some others are strict specialists and exclusively associate with a single photobiont variant. The most extensive symbiont network involves 24 different fungal species from five genera associating with 38 Nostoc photobionts. The Nostoc photobionts belong to two main groups, the Nephroma-type Nostoc and the Collema/Peltigera-type Nostoc, and nearly all mycobionts associate only with variants of one group. Among the mycobionts, species that produce cephalodia and those without symbiotic propagules tend to be most promiscuous in photobiont choice. The extent of photobiont sharing and the structure of interaction networks differ dramatically between the two major photobiont-mediated guilds, being both more prevalent and nested among Nephroma guild fungi and more compartmentalized among Peltigera guild fungi. This presumably reflects differences in the ecological characteristics and/or requirements of the two main groups of photobionts. The same two groups of Nostoc have previously been identified from many lichens in various lichen-rich ecosystems in different parts of the world, indicating that photobiont sharing between fungal species is an integral part of lichen ecology globally. In many cases, symbiotically dispersing lichens can facilitate the dispersal of sexually reproducing species, promoting establishment and adaptation into new and marginal habitats and thus driving evolutionary diversification.

Interactions within lichen communities include, in addition to close mutualistic associations between the main partners of specific lichen symbioses, also more elusive relationships between members of a wider symbiotic community. Here, we analyze association patterns of cyanolichen symbionts in the tropical montane forests of Taita Hills, southern Kenya, which is part of the Eastern Afromontane biodiversity hotspot. The cyanolichen specimens analyzed represent 74 mycobiont taxa within the order Peltigerales (Ascomycota), associating with 115 different variants of the photobionts genus Nostoc (Cyanobacteria). Our analysis demonstrates wide sharing of photobionts and reveals the presence of several photobiont-mediated lichen guilds. Over half of all mycobionts share photobionts with other fungal species, often from different genera or even families, while some others are strict specialists and exclusively associate with a single photobiont variant. The most extensive symbiont network involves 24 different fungal species from five genera associating with 38 Nostoc photobionts. The Nostoc photobionts belong to two main groups, the Nephroma -type Nostoc and the Collema / Peltigera -type Nostoc , and nearly all mycobionts associate only with variants of one group. Among the mycobionts, species that produce cephalodia and those without symbiotic propagules tend to be most promiscuous in photobiont choice. The extent of photobiont sharing and the structure of interaction networks differ dramatically between the two major photobiont-mediated guilds, being both more prevalent and nested among Nephroma guild fungi and more compartmentalized among Peltigera guild fungi. This presumably reflects differences in the ecological characteristics and/or requirements of the two main groups of photobionts. The same two groups of Nostoc have previously been identified from many lichens in various lichen-rich ecosystems in different parts of the world, indicating that photobiont sharing between fungal species is an integral part of lichen ecology globally. In many cases, symbiotically dispersing lichens can facilitate the dispersal of sexually reproducing species, promoting establishment and adaptation into new and marginal habitats and thus driving evolutionary diversification. [ABSTRACT FROM AUTHOR]

Lichen symbioses are microecosystems hosting many other living organisms besides the two major lichen symbionts (i.e., lichenized fungi [the mycobiont] and green microalgae or cyanobacteria [the photobiont]). Recent investigations evidenced that other fungi, non‐photosynthetic bacteria, and microalgae co‐inhabit within the lichen thalli, but their diversity and their roles are still underinvestigated. Here we present an ad hoc stratified sampling design and in‐depth Illumina paired‐end metabarcoding approach to explore microalgal diversity in lichen thalli of the model species Ramalina farinacea from different ecologies. Lichen thalli were surveyed according to three different sizes, and different thallus parts were considered for molecular, bioinformatics, and community diversity analyses. The results revealed that microalgal diversity strongly depends on the growth stage of the thalli, the geographic area, and the habitat type. The results also show that microalgal diversity does not vary along the thallus branches (lacinias)—that is, it does not correlate with the apical growth and founder effects—and that there is no balanced co‐presence of two main photobionts as previously established in R. farinacea. The sampling design performed here minimizes bias in the assessment of photobiont diversity in lichens and is proposed to be reliable and applicable to further study microalgal diversity in lichen symbioses. [ABSTRACT FROM AUTHOR]

Biodiversity varies with elevation and is affected by disturbances. However, little is known about how the associations between the diversities of different bryophyte and macrolichen functional-taxonomic groups are altered along elevational gradients and by disturbances. Knowledge on the associations between these functional-taxonomic groups might be of importance in practical conservation biology, as identifying indicator taxa which are easy to monitor could be useful in estimating a wider biodiversity. We sampled the species richness of bryophytes and macrolichens in 92 plots distributed in disturbed and undisturbed stands along elevational gradients in the laurel forest of Madeira. We then calculated a matrix of correlations for all pairwise combinations of 18 different functional-taxonomic bryophyte and macrolichen groups and tested for average differences in correlations with elevation and disturbance history and whether particular functional-taxonomic groups can be used to estimate the richness of other taxa. Associations between the diversities of functional-taxonomic groups within the bryophyte group and within the macrolichen group were always positive and mainly strong. Although changes in elevation and disturbance history changed the associations between the different bryophyte and macrolichen functional-taxonomic groups, we found the species richness of mosses or liverworts to be suitable for predicting overall bryophyte species richness and the species richness of green-algae macrolichens to be reliable for estimating overall macrolichen species richness. Associations between diversities of bryophyte and macrolichen groups were generally weak, suggesting that the two groups have different ecological requirements and do not share the same environmental drivers. The fact that no single bryophyte taxon can be used to predict the richness of any macrolichen group, and vice versa, points to the need to study both bryophytes and lichens. However, we found indicator taxa that are relatively easy to monitor and therefore could be used to estimate the wider biodiversity. [ABSTRACT FROM AUTHOR]

Lichens are classic models of symbiosis, and one of the most frequent nutritional modes among fungi. The ecologically and geographically widespread lichen-forming algal (LFA) genus Trebouxia is one of the best-studied groups of LFA and associates with over 7000 fungal species. Despite its importance, little is known about its diversification. We synthesized twenty years of publicly available data by characterizing the ecological preferences of this group and testing for time-variant shifts in climatic regimes over a distribution of trees. We found evidence for limited shifts among regimes, but that disparate lineages convergently evolved similar ecological tolerances. Early Trebouxia lineages were largely forest specialists or habitat generalists that occupied a regime whose extant members occur in moderate climates. Trebouxia then convergently diversified in non-forested habitats and expanded into regimes whose modern representatives occupy wet-warm and cool-dry climates. We rejected models in which climatic diversification slowed through time, suggesting climatic diversification is inconsistent with that expected under an adaptive radiation. In addition, we found that climatic and vegetative regime shifts broadly coincided with the evolution of biomes and associated or similar taxa. Together, our work illustrates how this keystone symbiont from an iconic symbiosis evolved to occupy diverse habitats across the globe. [ABSTRACT FROM AUTHOR]

This research work aimed at investigating the chemistry and biosynthetic potential of ascidian-associated symbionts that originated from Manado Bay, North Sulawesi. We initially enriched the symbiotic cells associated with the Manadonese ascidian Lissoclinum patella. Subsequently we identified the presence of Prochloron didemni in both unenriched and salt-enriched samples by examining the 16S rRNA gene and the chlorophyll A oxygenase (CAO) gene. Investigation of the secondary metabolites by HPLC, LCMS/MS, and NMR showed the presence of ulithiacyclamide along with patellamide E in the unenriched symbiotic cells. Interestingly, ulithiacyclamide was detected in the enriched cells from the same Ascidian specimen. Molecular docking showed the high binding affinity of both compounds to estrogen receptor beta (ER-β) protein. This is a subtype of the nuclear receptor superfamily expressed abnormally in ovarian cancer cells. Furthermore, we isolated a patE gene variant encoding for a precursor with patellamide E (VTVCITFC) and ulithiacyclamide (CTLCCTLC) core peptides from the enriched cells. This represents a new core peptide combination. The outcome of this work provides a basis for producing useful cyclic peptides, in sustainable way, through symbiont cultivation. This could become a platform for bioengineering to generate diverse compound analogues. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Spribille et al. (2022), 234: 1566–1582. [ABSTRACT FROM AUTHOR]

We evaluated and compared the physiological and morphological response to pollution of two epiphytic lichen species, the foliose lichen Flavopunctelia praesignis and the fruticose lichen Usnea ceratina. Lichen samples were collected at remote areas and transplanted at different distances and directions from a paper industry in Morelia (Michoacán, Mexico). Lichen transplants were exposed for 4 months (1) around the industrial area and (2) in their native habitats (control sites). Changes of total chlorophyll content between samples before and after exposure, and morphological damage in the lichen thalli were investigated. Lichens showed species-specific responses. Flavopunctelia praesignis increased in total chlorophyll content after exposure around the industrial area and in control site. This suggests that total chlorophyll changes by a seasonal effect than pollution effect. On the other hand, chlorophyll content of U. ceratina did not change significantly after exposure. Bleaching, changes in color, deformations, and necrosis of lichen thalli were better visible in U. ceratina near the paper industry. We conclude that U. ceratina is a more pollution-sensitive species than F. praesignis. Morphological damage in the lichen thalli would be a suitable indicator for monitoring early biological effects of air pollution caused by the paper industry. [ABSTRACT FROM AUTHOR]

Lichens are remarkable and classic examples of symbiotic organisms that have fascinated scientists for centuries. Yet, it has only been for a couple of decades that significant advances have focused on the diversity of their green algal and/or cyanobacterial photobionts. Cyanolichens, which contain cyanobacteria as their photosynthetic partner, include up to 10% of all known lichens and, as such, studies on their cyanobionts are much rarer compared to their green algal counterparts. For the unicellular cyanobionts, i.e. cyanobacteria that do not form filaments, these studies are even scarcer. Nonetheless, these currently include at least 10 different genera in the cosmopolitan lichen order Lichinales. An international consortium (International Network of CyanoBionts; INCb) will tackle this lack of knowledge. In this article, we discuss the status of current unicellular cyanobiont research, compare the taxonomic resolution of photobionts from cyanolichens with those of green algal lichens (chlorolichens), and give a roadmap of research on how to recondition the underestimated fraction of symbiotic unicellular cyanobacteria in lichens., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the International Society for Microbial Ecology.)

The reproduction and dispersal strategies of lichens play a major role in shaping their population structure and photobiont diversity. Sexual reproduction, which is common, leads to high lichen genetic diversity and low photobiont selectivity. However, the lichen genus Endocarpon adopts a special co-dispersal model in which algal cells from the photobiont and ascospores from the mycobiont are released together into the environment. To explore the dispersal strategy impact on population structures, a total of 62 Endocarpon individuals and 12 related Verrucariaceae genera individuals, representing co-dispersal strategy and conventional independent dispersal mode were studied. Phylogenetic analysis revealed that Endocarpon , with a large-scale geographical distribution, showed an extremely high specificity of symbiotic associations with their photobiont. Furthermore, three types of group I intron at 1769 site have been found in most Endocarpon mycobionts, which showed a high variety of group I intron in the same insertion site even in the same species collected from one location. This study suggested that the ascospore-alga co-dispersal mode of Endocarpon resulted in this unusual mycobiont-photobiont relationship; also provided an evidence for the horizontal transfer of group I intron that may suggest the origin of the complexity and diversity of lichen symbiotic associations., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (2024, by The Mycological Society of Japan.)

Lichens are fungi (mycobionts) that form symbiotic associations with photoautotrophic prokaryotes or eukaryotes (photobionts); however, some species can exchange photosynthetic partners during their lifecycles. This phenomenon modifies the morphology of lichens and consequently influences the taxonomy of lichenized fungi. Here, a few such cases in which the photobionts influenced the taxonomy and systematics of lichenized fungi are reviewed. Two different morphotypes of the same species – known as photomorphs – were classified as different species and sometimes different genera. Moreover, different types of photobionts and the absence or presence (optional lichenization) of an alga in the thallus were believed to be diagnostic characters for discriminating genera. However, the taxonomy and systematics of lichens are based always, according to Article F.1.1. of the International Code of Nomenclature for Algae, Fungi, and Plants, on the fungal partner and only one name is applied.

Lichens are fungi (mycobionts) that form symbiotic associations with photoautotrophic prokaryotes or eukaryotes (photobionts); however, some species can exchange photosynthetic partners during their lifecycles. This phenomenon modifies the morphology of lichens and consequently influences the taxonomy of lichenized fungi. Here, a few such cases in which the photobionts influenced the taxonomy and systematics of lichenized fungi are reviewed. Two different morphotypes of the same species - known as photomorphs - were classified as different species and sometimes different genera. Moreover, different types of photobionts and the absence or presence (optional lichenization) of an alga in the thallus were believed to be diagnostic characters for discriminating genera. However, the taxonomy and systematics of lichens are based always, according to Article F.1.1. of the International Code of Nomenclature for Algae, Fungi, and Plants, on the fungal partner and only one name is applied. [ABSTRACT FROM AUTHOR]

Asterochloris is one of the most common genera of lichen phycobionts in Trebouxiophyceae. Asterochloris phycobionts associated with the lichenized fungi Cladonia and Stereocaulon in King George Island (Antarctica) and Morro Chico (Chile), were isolated and then used to establish clonal cultures. To understand the phylogenetic relationships and species diversity of Antarctic Asterochloris species, molecular and morphological data were analyzed by using three microscopy techniques (light, confocal laser and transmission electron) and a multi-locus phylogeny with data from the nuclear-encoded internal transcribed spacer (ITS) rDNA and the actin and plastid-encoded ribulose bisphosphate carboxylase large chain (rbcL) coding genes. Morphological data of three Antarctic strains showed significant speciesspecific features in chloroplast while molecular data segregated the taxa into distinct three clades as well. Each species had unique molecular signatures that could be found in secondary structures of the ITS1 and ITS2. The species diversity of Antarctic Asterochloris was represented by six taxa, namely, A. glomerata, A. italiana, A. sejongensis, and three new species (A. antarctica, A. pseudoirregularis, A. stereocaulonicola). [ABSTRACT FROM AUTHOR]

Background and Aims Lichens represent a symbiotic relationship between at least one fungal and one photosynthetic partner. The association between the lichen-forming fungus Mastodia tessellata (Verrucariaceae) and different species of Prasiola (Trebouxiophyceae) has an amphipolar distribution and represents a unique case study for the understanding of lichen symbiosis because of the macroalgal nature of the photobiont, the flexibility of the symbiotic interaction and the co-existence of free-living and lichenized forms in the same microenvironment. In this context, we aimed to (1) characterize the photosynthetic performance of co-occurring populations of free-living and lichenized Prasiola and (2) assess the effect of the symbiosis on water relations in Prasiola , including its tolerance of desiccation and its survival and performance under sub-zero temperatures. Methods Photochemical responses to irradiance, desiccation and freezing temperature and pressure–volume curves of co-existing free-living and lichenized Prasiola thalli were measured in situ in Livingston Island (Maritime Antarctica). Analyses of photosynthetic pigment, glass transition and ice nucleation temperatures, surface hydrophobicity extent and molecular analyses were conducted in the laboratory. Key Results Free-living and lichenized forms of Prasiola were identified as two different species: P. crispa and Prasiola sp. respectively. While lichenization appears to have no effect on the photochemical performance of the alga or its tolerance of desiccation (in the short term), the symbiotic lifestyle involves (1) changes in water relations, (2) a considerable decrease in the net carbon balance and (3) enhanced freezing tolerance. Conclusions Our results support improved tolerance of sub-zero temperature as the main benefit of lichenization for the photobiont, but highlight that lichenization represents a delicate equilibrium between a mutualistic and a less reciprocal relationship. In a warmer climate scenario, the spread of the free-living Prasiola to the detriment of the lichen form would be likely, with unknown consequences for Maritime Antarctic ecosystems. [ABSTRACT FROM AUTHOR]