UV triggers the synthesis of the widely distributed secondary lichen compound usnic acid

Synthesis of the cortical dibenzofuran derivative usnic acid and the medullary depsidone salazinic acid was studied in Xanthoparmelia stenophylla thalli from which the compounds had been removed by acetone rinsing prior to a 21-day field experiment with UV absorbing and transmitting screens. Natural levels of ultraviolet radiation clearly induced the re-synthesis of usnic acid. The re-synthesis was boosted by the addition of ribitol, the carbohydrate delivered from the Trebouxia photobiont to the mycobiont. Salazinic acid was also weakly induced by UV. Re-synthesis was relatively low, up to 2.5 and 3.1% of start values for usnic and salazinic acid, respectively. However, given that the natural content of both compounds was high, constituting 12% of thallus dry weight, the absolute amounts of lichen compounds re-synthesised were not so small. We also studied the extractability of nine extracellular lichen compounds in three species X. stenophylla, Hypogymnia tubulosa, and Vulpicida pinastri, and found two distinct fractions of cortical compounds, one major that was completely extractable from living lichens and one minor that was only extractable with grinding. Medullary compounds were completely extracted without grinding. These findings did not influence the relative differences between treatments in our experiment, but may be of importance for future assessments of, e.g., quantitative studies of extracellular lichen compounds.     

POROSIMETRIC STUDY OF THE LICHEN FAMILY UMBILICARIACEAE: ANATOMICAL INTERPRETATION AND IMPLICATIONS FOR WATER STORAGE CAPACITY OF THE THALLUS

The pore system within the thalli of 13 lichen taxa belonging to the family Umbilicariaceae has been studied by means of mercury intrusion porosimetry. A characteristic bimodal pore size distribution with a central depression around 0.05 μm of equivalent pore radius was obtained in all lichen samples. However, clear differences were found among the pore size distributions of each lichen taxa. The total thallus porosity was undoubtedly related to the anatomy of the medulla. In general, a radial plectenchymatic medulla conferred larger porosity to the thallus than an arachnoidal one. Maximum thallus water content closely depended on the total thallus porosity in the five lichens possessing rhizinomorphs. The species with a similar type of medulla could be grouped together in a multivariate analysis that considered three porosimetric parameters and the maximum thallus water content. Umbilicaria cinereorufescens was the most distinct species, with the lowest values of total porosity and water storage capacity and the largest value of thallus density, apparently due to its scleroplectenchymatic medulla. The pore size distribution existing inside the thallus of the species studied is discussed in relation to the often opposing problems of CO₂ exchange and optimal water relations. Some results pointed to a large influence of the micropores (<0.05 μm) on the water storage capacity of the thallus, while the macropores would have a more important role in gas exchange.     

Secondary chemistry of cultured mycobionts: formation of a complete chemosyndrome by the lichen fungus of Lobaria spathulata

Abstract:The study aimed to optimize culture conditions and nutrient requirements for the production of secondary metabolites by the cultured mycobiont Lobaria spathulata. This species proved to be an excellent model system for such studies, as the complete chemosyndrome found in the natural lichen thallus was repeatedly formed in the cultured mycobiont with differentiated, aerial mycelia. Nutrient media containing the disaccharide, sucrose, were found to favour both rapid growth and the production of typical lichen substances. Higher proportions of the secondary compounds were detected in the developing mycobiont than in mature lichen thalli.     

The significance of thallus size for the water economy of the cyanobacterial old-forest lichen Degelia plumbea

Rosette-formed, circular thalli of Degelia plumbea were studied in the laboratory. Regardless of thallus size, the optimal quantum yield of photosystem II (F _V/F _M) remained at a high, constant level during a drying cycle starting with fully hydrated thalli until the thallus water content reached about 200%. Net photosynthesis reached a maximum level at this hydration level. Thereafter, both F _V/F _M and net photosynthesis fell rapidly to zero at a water content of somewhat less than 100%. There was a highly significant, positive relationship between thallus size and the water-holding capacity, as well as a strong, negative correlation between size and water loss per thallus area. Consequently, an increase in thallus size from 1 to 36 cm² lead to a tenfold prolongation of the photosynthetically active period during a drying cycle at a low radiation regime. The improved water-holding capacity in larger thalli is mainly a result of a thicker hypothallus. The fast desiccation of small thalli suggests that the regeneration of D. plumbea could be severely hampered by nearby logging that raises the evaporative demand by increasing radiation loads and wind exposure at remaining lichen sites. Received: 12 December 1997 / Accepted: 20 March 1998     

Influence of sun irradiance and water availability on lichen photosynthetic pigments during a Mediterranean summer

This study was carried out to investigate changes in lichen photosynthetic pigments induced by different combinations of light irradiance and water availability during a Mediterranean summer. To this purpose, thalli of three epiphytic lichens with a markedly different ecology concerning photo-hygrophytism, namely Evernia prunastri (hygro-mesophytic), Flavoparmelia caperata (mesophytic) and Xanthoria parietina (xero-mesophytic), were transplanted for 30 days to N- and S-facing cardinal exposures in central Italy. To investigate the effect of thallus hydration, at each cardinal exposure 50% of thalli were hydrated daily with deionised water. The results showed that changes in the concentrations of photosynthetic pigments are species-specific and consist in a general depression of photosynthetic pigments only in the hygro-mesophytic species E. prunastri. The pattern of photosynthetic pigments was also investigated in spontaneous samples along contrasting aspects. In this case, X. parietina from S-facing slopes, adapted to direct solar influx, showed higher pigment content than N-facing thalli; F. caperata and E. prunastri avoid direct extreme solar radiation and assimilation pigments were influenced more by the shadowing of tree canopies than by the cardinal exposure. The influence of drought on lichen photosynthetic pigments in the Mediterranean area is discussed.     

Developmental stages and secondary compound biosynthesis of mycobiont and whole thallus cultures of <Emphasis Type="Italic">Buellia subsororioides</Emphasis>

Lichen species have unique culture media preferences, and established cultures are known for the synthesis of secondary metabolites. This paper reports observations on the developmental stages and secondary compound biosynthesis by the mycobiont and whole thallus cultures of Buellia subsororioides. It also investigates the suitable media compositions for the culture growth, the role (nutrient or stressor) of sucrose concentrations on the growth stages, biomass, secondary compound profiles, and the quantity of biosynthesized known compounds/g of culture biomass for each treatment using mycobiont cultures. The ascospore-derived mycobiont cultures and thallus macerate-derived whole thallus cultures of B. subsororioides were established and grown using malt yeast extract (MY) medium. Mycobiont cultures were subcultured in MY medium supplemented with sucrose and its concentrations ranging from 0 to 30 % (with 2 % increment between treatments) for 120 days. The molecular identity of cultures was confirmed using nuclear ribosomal Internal transcribed spacer (ITS) DNA sequences obtained from the cultured mycobiont and from the natural thallus. The ITS DNA sequences of the mycobiont showed 99 % similarity with the sequences of the natural thallus. The mycobiont cultures under varying sucrose concentrations initiated as white cottony stages and transformed to brown compact mycelia, with optimum biomass and biosynthesis of nine secondary compounds in MY 10 %. The number of compounds (1–9) varies according to treatments. The whole thallus cultures (MY 0 %) showed a profile of secondary compounds similar to that of the natural thalli along with a trace of one unknown compound. The obtained results are encouraging for the synthesis of the desired quantities of lichen secondary compounds through cultures for relevant applications.     

Do secondary substances in the thallus of a lichen promote CO2 diffusion and prevent depression of net photosynthesis at high water content?

Many lichens show seriously depressed net photosynthesis (NP) at high thallus water contents due to increased carbon dioxide diffusion resistance through blockage of diffusion pathways by water. The soil lichen Diploschistes muscorum, however, shows no depression and NP is close to maximal even at the highest thallus water content. We investigated whether lichen substances (lecanoric and diploschistesic acids) in the cortex and medulla contributed to this ability to maintain high NP. Dry thalli were extracted with water-free acetone and, after this treatment, were found to be fully viable to the extent of continued growth after replanting in the field. No differences were found in the response of NP to thallus water content between the normal and extracted thalli, in fact the response curves were often nearly identical. Thus, in this species it seems that lichen substances did not maintain the water-free diffusion pathways and some other explanation, possibly structural, needs to be sought. Received: 5 April 1997 / Accepted: 26 April 1997     

Possible functional roles of cortical depsides and medullary depsidones in the foliose lichen Hypogymnia physodes

Secondary compounds were quantified in 75 thalli of the foliose lichen Hypogymnia physodes collected in habitats along a natural shade-sun gradient from dark spruce forests to sun-exposed sea cliffs. The irradiance in all the 75 lichen sites was estimated from hemispherical photographs. The content of lichen compounds per thallus area correlated positively with irradiance level (r²=0.73), and the mean concentration increased from 6.7% in the spruce forest to 14.4% on sea cliffs. The medullary depsidones, physodic, physodalic and protocetraric acids, constituted >95% of the total pool of extractable secondary compounds, the cortical depsides, atranorin and chloratranorin, represented <5%. Both cortical compounds correlated well with direct and with diffuse radiation, whereas the three medullary compounds correlated better with diffuse than with direct radiation. Mentioned trends are consistent with a solar radiation screening hypothesis of both groups of these colourless compounds occuring as tiny crystals outside fungal hyphae. However, the UV-B protective hypothesis of the compounds was further tested in a lab experiment. Unnaturally high UV-B doses were required to significantly reduce the PSII efficiency (F_V/F_M) of symbiotic algae. Removal of the major pool of secondary compounds with acetone did not increase photobiont susceptibility to UV-B. Therefore, the main functional role of the UV-B absorbing secondary compounds in H. physodes is hardly UV-B screening. Other roles such as PAR-screening and defence against herbivores and pathogenic organisms are discussed.     

DOES TREE AGE PREDICT THE OCCURRENCE AND ABUNDANCE OF USNEA LONGISSIMA IN MULTI-AGED SUBMONTANE PICEA ABIES STANDS?

In boreal Scandinavia Usnea longissima is a rare epiphytic lichen associated with old spruce (Picea abies) forests. To test whether tree age was an important determinant of the occurrence and abundance of U. longissima at the scale of a forest stand we estimated thallus numbers on 1008 trees within three submontane spruce stands in south-central Norway. The stands were of all ages and multi-layered and had been selectively cut previous to the 1940s. There was no relationship between number of U. longissima thalli and tree age among trees with dbh of ≥10 cm. The most consistent pattern was a positive relationship between occurrence and number of thalli and stem diameter. After controlling the covariance of stem diameter, there was a tendency for a negative relationship between number of thalli and tree age. The results suggest that in old-growth resembling stands, with already established U. longissima populations, tree size (here measured as stem diameter) is a better predictor of thallus number than tree age. This does not contradict the possibility that other environmental characteristics, associated with stands of older age, may be important for the establishment and growth of U. longissima populations.     

Escape from the cryptic species trap: lichen evolution on both sides of a cyanobacterial acquisition event

Large, architecturally complex lichen symbioses arose only a few times in evolution, increasing thallus size by orders of magnitude over those from which they evolved. The innovations that enabled symbiotic assemblages to acquire and maintain large sizes are unknown. We mapped morphometric data against an eight‐locus fungal phylogeny across one of the best‐sampled thallus size transition events, the origins of the Placopsis lichen symbiosis, and used a phylogenetic comparative framework to explore the role of nitrogen‐fixing cyanobacteria in size differences. Thallus thickness increased by >150% and fruiting body core volume increased ninefold on average after acquisition of cyanobacteria. Volume of cyanobacteria‐containing structures (cephalodia), once acquired, correlates with thallus thickness in both phylogenetic generalized least squares and phylogenetic generalized linear mixed‐effects analyses. Our results suggest that the availability of nitrogen is an important factor in the formation of large thalli. Cyanobacterial symbiosis appears to have enabled lichens to overcome size constraints in oligotrophic environments such as acidic, rain‐washed rock surfaces. In the case of the Placopsis fungal symbiont, this has led to an adaptive radiation of more than 60 recognized species from related crustose members of the genus Trapelia. Our data suggest that precyanobacterial symbiotic lineages were constrained to forming a narrow range of phenotypes, so‐called cryptic species, leading systematists until now to recognize only six of the 13 species clusters we identified in Trapelia.     

The occurrence of biomineralization products in four lichen species growing on sandstone in western Norway

High performance thin-layer chromatography/thin-layer chromatography, X-ray diffraction, and scanning electron microscopy analysis of thallus and lichen-rock interface samples, were undertaken to characterize biomineralization products in Fuscidea cyathoides, Ochrolechia tartarea, Ophioparma ventosa, and Pertusaria corallina, growing on sandstone in western Norway. Whewellite (monohydrate form of Ca oxalate) was found in the thallus of all species, but not in any of the weathering rinds beneath the species. A significantly higher amount of whewellite was detected in the thalli of F. cyathoides and O. ventosa than in the other two species. There were only a few differences in whewellite occurrence between the thallus edge and centre samples in the four species. HPTLC/TLC and SEM analysis indicate that lichen compounds occur within the rock beneath some of the lichen specimens. Only divaricatic acid was observed within the weathering rind beneath O. ventosa. No lichen substances were found in the weathering rind beneath F. cyathoides and P. corallina, whereas gyrophoric and lecanoric acids were found in the weathering rind beneath O. tartarea.     

Juvenile Development and Diaspore Survival in the Threatened Epiphytic Lichen Species Sticta fuliginosa, Leptogium saturninum and Menegazzia terebrata: Conclusions for in situ Conservation

Abstract: Development and growth of the three threatened epiphytic lichen species Sticta fuliginosa (Hoffm.) Ach., Leptogium saturninum (Dicks.) Nyl. and Menegazzia terebrata (Hoffm.) Massal. was investigated by low temperature scanning electron microscopy and macro‐photography. Small cotton gauze discs acting as artificial substrata were fixed with aluminium staples on the bark of selected trees and vegetative diaspores (isidia or soredia) were transferred onto these discs. The subsequent development into small thalli of up to 3 mm length was observed within the 32‐month study period. All three species produced anchoring hyphae within the first month after transplantation. Two months later 52 % of the S. fuliginosa diaspores were still on the gauze discs and after 16 months 29 % remained attached. For L. saturninum, the corresponding percentages were 46 % and 19 %, respectively. First lobes resembling adult thalli were observed after 8 to 12 months in S. fuliginosa and L. saturninum but only after 16 months in M. terebrata. All three species developed usually more than one thallus primordium (pseudomeristematic growth zone) per isidium or soredial cluster. Transplanted thallus fragments were able to fix themselves on the new substratum but in all three species large parts degenerated and fell off during the first year, particularly in S. fuliginosa. The results show that the juvenile development of the investigated species is not restricted by microclimatic factors at the study site. We therefore conclude that the juvenile development is not the restricting factor in regard to growth and population survival. Other factors, such as the competition with bryophytes, insufficient diaspore dispersal or forest management practice must account for the small population sizes. The described transplantation technique of vegetative diaspores has proved to be very useful for the augmentation of small populations without damaging the existing thalli and we suggest use of this method for in situ conservation of endangered lichen species.     

Heterogeneity of Chlorophyll Fluorescence over Thalli of Several Foliose Macrolichens Exposed to Adverse Environmental Factors: Interspecific Differences as Related to Thallus Hydration and High Irradiance

Spatial heterogeneity of chlorophyll (Chl) fluorescence over thalli of three foliose lichen species was studied using Chl fluorescence imaging (CFI) and slow Chl fluorescence kinetics supplemented with quenching analysis. CFI values indicated species-specific differences in location of the most physiologically active zones within fully hydrated thalli: marginal thallus parts (Hypogymnia physodes), central part and close-to-umbilicus spots (Lasallia pustulata), and irregulary-distributed zones within thallus (Umbilicaria hirsuta). During gradual desiccation of lichen thalli, decrease in Chl fluorescence parameters (F_O - minimum Chl fluorescence at point O, F_P - maximum Chl fluorescence at P point, ₂ - effective quantum yield of photochemical energy conversion in photosystem 2) was observed. Under severe desiccation (>85 % of water saturation deficit), substantial thalli parts lost their apparent physiological activity and the resting parts exhibited only a small Chl fluorescence. Distribution of these active patches was identical with the most active areas found under full hydration. Thus spatial heterogeneity of Chl fluorescence in foliose lichens may reflect location of growth zones (pseudomeristems) within thalli and adjacent newly produced biomass. When exposed to high irradiance, fully-hydrated thalli of L. pustulata and U. hirsuta showed either an increase or no change in F_O, and a decrease in F_P. Distribution of Chl fluorescence after the high irradiance treatment, however, remained the same as before the treatment. After 60 min of recovery in the dark, F_O and F_P did not recover to initial values, which may indicate that the lichen used underwent a photoinhibition. The CFI method is an effective tool in assessing spatial heterogeneity of physiological activity over lichen thalli exposed to a variety of environmental factors. It may be also used to select a representative area at a lichen thallus before application of single-spot fluorometric techniques in lichens.     

Surface hydrophobicity causes SO2 tolerance in lichens

BACKGROUND AND AIMS: The superhydrophobicity of the thallus surface in one of the most SO(2)-tolerant lichen species, Lecanora conizaeoides, suggests that surface hydrophobicity could be a general feature of lichen symbioses controlling their tolerance to SO(2). The study described here tests this hypothesis. METHODS: Water droplets of the size of a raindrop were placed on the surface of air-dry thalli in 50 lichen species of known SO(2) tolerance and contact angles were measured to quantify hydrophobicity. KEY RESULTS: The wettability of lichen thalli ranges from strongly hydrophobic to strongly hydrophilic. SO(2) tolerance of the studied lichen species increased with increasing hydrophobicity of the thallus surface. Extraction of extracellular lichen secondary metabolites with acetone reduced, but did not abolish the hydrophobicity of lichen thalli. CONCLUSIONS: Surface hydrophobicity is the main factor controlling SO(2) tolerance in lichens. It presumably originally evolved as an adaptation to wet habitats preventing the depression of net photosynthesis due to supersaturation of the thallus with water. Hydrophilicity of lichen thalli is an adaptation to dry or humid, but not directly rain-exposed habitats. The crucial role of surface hydrophobicity in SO(2) also explains why many markedly SO(2)-tolerant species are additionally tolerant to other (chemically unrelated) toxic substances including heavy metals.     

Population dynamics of the lichen genus Bulbothrix Hale as potential bioindicators of 'time-since-last-fire' in the cerrado of the Distrito Federal, central Brazil

This paper investigates the potential use of the corticolous lichen genus Bulbothrix Hale as a bioindicator of ‘time-since-last-fire’ in the cerrado (savannas) of central Brazil. Work was carried out at the Reserva Ecológica do IBGE and the Jardim Botãnico de Brasilia, 33 km outside Brasilia D.F., in plots of cerrado denso with known fire histories within the ‘Fire Project’ area. Measurements of abundance and thallus size were taken of all Bulbothrix individuals encountered up to 2 m on the trunks of three phorophyte species. The results show that abundances and thalli sizes of the Bulbothrix populations can be correlated with the ‘time-since-last-fire’ that had occurred in each of the plots. This study shows that is is possible to use characteristics of specific lichen populations as bioindicators of fire history.     

Light might regulate divergently depside and depsidone accumulation in the lichen Parmotrema hypotropum by affecting thallus temperature and water potential

Depsides and depsidones are the most common secondary products uniquely produced in lichens by the fungal symbiont, and they accumulate on the outer surface of its hyphae. Their biological roles are subject to debate. Quantitatively the compounds typical of a given lichen can vary dramatically from thallus to thallus. Several studies have addressed whether this variability is correlated with the light reaching different thalli, but the conclusions are contradictory. We addressed the question with the lichen Parmotrema hypotropum growing on unshaded, vertical tree trunks, a controlled natural environment where the light absorbed by each thallus over its lifetime is the only major position-dependent variable. The exact north-east-south-west orientation of each thallus was used to calculate its yearly light exposure based on astronomical and meteorological considerations. The calculated irradiation around the trunk, distributed over a continuous 40-fold intensity range, then was compared with the amount of compound per unit thallus weight, determined by quantitative thin layer chromatography. P. hypotropum accumulates the depside atranorin in the cortex and the depsidone norstictic acid in the medulla and around the algae. A direct correlation was observed between the yearly amount of light reaching the lichen and the amount of atranorin. In contrast, the amount of norstictic acid decreased with increasing light. Although we did not measure thallus temperature and water potential, a unifying interpretation of these and other published data is that depside/depsidone accumulation in lichens is mediated by localized changes in temperature and water potential produced by light absorption within each thallus. This suggests water relations-based functions for depsides and depsidones.     

Structural Aspects of the Lichen-Rock Interface Using Back-scattered Electron Imaging

The profound knowledge of the structural and chemical characteristics of the interface between lichen thallus and rock, seems to be indispensable for the process of understanding the lichen symbiosis as well as the significance of the weathering action of lichens. One of the most promising techniques to be used in this investigation is the Scanning Electron Microscopy (SEM) in the back-scattered electron (BSE) emission mode. In the present work thalli of Parmelia conspersa, Aspicilia intermutans and Lecidea auriculata growing in granitic rock were examined by SEM in BSE mode with (Energy Dispersive Spectroscopy) EDS. In the case of the foliose thalli the observation of the interface permits detection of the rhizine/hyphae adherence and determination of the origin of the minerals which adhere to the rhizine/hyphae. In the case of the crustose thalli BSE permits investigation within the ultrastructure of the crustose thallus and crustose lichen-rock contact zone and also allows observations of the penetration and filling of the fissures and cracks of the underlying rock by components of the thallus and other living organisms. The BSE images could contribute to a better knowledge of the cytological state of the rock-inhabiting organisms and also to the understanding of the action of the chemical treatments used in the removal of lichen from building materials.     

PHENOTYPIC VARIATION WITHIN “INDIVIDUAL” LICHEN THALLI

“Individual” large diam lichen thalli of Umbilicaria vellea (L.) Ach. and U. mammulata (Ach.) Tuck. are not uniform in physiological activity or enzymatic phenotype. Horizontal variation in net photosynthetic rates and dark respiration rates was found, but this was independent of the mass of the photosynthesizing or respiring tissues. In addition, sublethal temperature pretreatments reduced the net photosynthetic and respiratory rates of some areas of the thallus, but increased others. Assays of isoenzyme phenotypes showed that all large diam thalli are extensively polymorphic while young, small diam thalli are mainly monomorphic. Taken together, the results say that the concept of the “individual” may be inappropriate for these organisms.     

Neuroprotective activity and cytotoxic potential of two Parmeliaceae lichens: Identification of active compounds

BackgroundLichens are symbiotic organisms capable of producing unique secondary metabolites, whose pharmacological activities are attracting much interest.PurposeThe present study aimed to investigate the in vitro neuroprotective effects and anticancer potential of methanol extracts of two Parmeliaceae lichens: Cetraria islandica and Vulpicida canadensis. The chemical composition of the two lichens was also determined.MethodsNeuroprotective activity was studied with respect to the antioxidant properties of the extracts; radical scavenging tests (ORAC and DPPH assays) were performed and oxidative stress markers (intracellular ROS production, caspase-3 activity, MDA and glutathione levels) were assessed in a hydrogen peroxide-induced oxidative stress model in astrocytes. Cytotoxic activity was tested against human HepG2 (hepatocellular carcinoma) and MCF-7 (breast adenocarcinoma) cell lines.ResultsCell viability studies identified a single concentration for each extract that was subsequently used to measure oxidative stress markers. Lichen extracts were able to reverse the oxidative damage caused by hydrogen peroxide, thus promoting astrocyte survival. Both lichen extracts also had anticancer activity in the cell lines, with IC₅₀ values of 19.51–181.05 µg/ml. The extracts had a high total phenolic content, and the main constituents identified by HPLC were fumarprotocetraric acid in Cetraria islandica, and usnic, pinastric and vulpinic acids in Vulpicida canadensis. The biological activities of the lichen extracts can be attributed to these secondary metabolites.ConclusionThe lichen species studied are promising sources of natural compounds with neuroprotective activity and cytotoxic potential, and warrant further research.     

Lichen palatability depends on investments in herbivore defence

Lichens are well-suited organisms for experimental herbivory studies because their secondary compounds, assumed to deter grazing, can be non-destructively extracted. Thalli of 17 lichen species from various habitats were cut in two equal parts; compounds were extracted from one part by acetone, the other served as a control. These two pieces were offered as a paired choice to the generalist herbivore snail Cepaea hortensis. Control thalli of all lichens were consumed at a low rate regardless of their investments in acetone-extractable lichen compounds; naturally compound-deficient lichen species were not preferred compared to those with high contents. However, for extracted thalli, there was a highly significant positive correlation between rate of consumption and the extracted compound contents. These data imply that herbivore defence has evolved in different directions in different lichens. Studied members of Parmeliaceae, common in oligotrophic habitats, have high contents of carbon-rich acetone-soluble compounds; these lichens became highly palatable to snails subsequent to acetone rinsing. Extracted lichen compounds were applied to pieces of filter paper and fed to snails. Extracts from members of the Parmeliaceae significantly deterred feeding on paper. Such data suggest that generalist herbivores may have shaped evolution in the widespread and highly diverse Parmeliaceae towards high investments in lichen compounds. On the other hand, lichens belonging to the Physciaceae and Teloschistales, common in nutrient-enriched habitats, are deficient in, or have low concentrations of, lichen compounds. Such lichens did not become more palatable after acetone rinsing. The orange anthraquinone compound parietin, restricted to the Teloschistales, and which has previously been found to protect against excess light, did not deter grazing.