Evernia prunastri
(Wikimedia)1
Evernia prunastri (close-up)
(Wikimedia)2
Oakmoss (Evernia prunastri)
(Wikimedia)3
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Evernia prunastri (Wikimedia)1 |
Evernia prunastri (close-up) (Wikimedia)2 |
Oakmoss (Evernia prunastri) (Wikimedia)3 |
Lichens represent a fascinating and ecologically significant group of symbiotic organisms, typically formed through a mutualistic association between a fungus (mycobiont) and one or more photosynthetic partners, which can be green algae or cyanobacteria.[1] This intricate biological partnership enables lichens to colonize and thrive in a remarkable diversity of environments, ranging from temperate forests to exposed rock surfaces, demonstrating exceptional resilience.[1] Beyond their ecological adaptability, lichens are increasingly recognized for their capacity to synthesize a vast array of unique natural products, many of which exhibit substantial biological activities. This chemical richness positions them as valuable resources for various industries, including pharmaceuticals, cosmetics, and the food sector.[2] Moreover, their widespread occurrence and distinctive physiological characteristics render lichens indispensable tools for environmental monitoring, particularly owing to their acute sensitivity to atmospheric pollutants, making them effective bioindicators.[5]
Among these diverse organisms, Evernia prunastri, commonly known as Oakmoss, stands out as a prominent species of fruticose lichen, characterized by its branched, bushy thallus.[8] This species is widely distributed across mountainous temperate forests throughout the Northern Hemisphere, predominantly found adhering to the trunks and branches of oak trees, though it also commonly colonizes the bark of other deciduous trees and conifers such as fir and pine.[1] Historically, Oakmoss has been highly prized, especially within the perfumery industry, for its distinct and complex odor. This fragrance is frequently described as woody, sharp, and subtly sweet, with specimens growing on pines exhibiting a pronounced turpentine note that is particularly sought after in specific perfume compositions. Its unique olfactory profile makes it a foundational component in the Fougère and Chypre fragrance families, where it also serves as an excellent fixative base, prolonging the longevity of other scent components.[8] The traditional utility of Evernia prunastri extends beyond perfumery; historical records indicate its notable use by ancient Egyptians for making bread, underscoring its long-standing significance as an edible and functional food source.[1] Furthermore, the secondary metabolites produced by E. prunastri have been empirically utilized in folk medicine and as natural dyes for centuries.[13]
A compelling aspect of Evernia prunastri is its seemingly paradoxical environmental role. While it exhibits a wide ecological amplitude and is often abundant across its distribution, thriving in well-lit, exposed conditions on various barks, it simultaneously demonstrates profound sensitivity to specific environmental stressors, notably sulfur dioxide (SO2) and ammonia pollution.[5] This characteristic positions E. prunastri as a dynamic sentinel species. Its widespread occurrence makes it a readily accessible and practical biomonitor, yet its acute physiological sensitivity means that its decline or subsequent recolonization provides critical, real-time feedback on air quality improvements or degradations. For instance, its rapid return to urban areas following reductions in SO2 levels, as observed in the English Midlands, illustrates its capacity to reflect environmental recovery.[5] This dual nature—being both a robust survivor in diverse habitats and a delicate indicator of environmental health—highlights its unique value for both ecological assessment and the evaluation of environmental policy effectiveness.
Evernia prunastri is formally classified within the biological hierarchy as follows: Domain: Eukaryota, Kingdom: Fungi, Division: Ascomycota, Class: Lecanoromycetes, Order: Lecanorales, Family: Parmeliaceae, and Genus: Evernia.[9] Its accepted binomial name is Evernia prunastri (L.) Ach., established in 1810.[9] Historical synonyms include Lichen prunastri L. (1753) and Evernia prunastri f. herinii (Duvign.) D. Hawksw. (1980), with the latter denoting a distinct grey variant characterized by its deficiency in usnic acid.[9]
Morphologically, Evernia prunastri is categorized as a fruticose lichen, distinguished by its branched, bushy thalli.[8] The thallus comprises strap-shaped lobes that frequently appear twisted and pendulous, typically measuring between 1 and 10 cm in length, 2 to 6 mm in width, and approximately 1 mm in thickness.[6] A key diagnostic feature is the pronounced color difference between its surfaces: the upper surface varies from green-grey to pale green-yellow, while the lower surface is predominantly white.[6] This striking contrast is attributed to its internal foliose structure, which features a single layer of algal cells situated directly beneath the upper cortex.[6] Specialized reproductive structures known as soredia become abundant on the upper surface, initially appearing rounded and often confined to eroded areas of ridges or lobe margins, eventually coalescing to form larger patches.[14] An incomplete network of elongate ridges may also be discernible on the upper thallus surface.[6] While rare in Britain, apothecia (fruiting bodies) can occur, typically measuring 2–5 mm in diameter, with ascospores of 7–11 x 4–6 μm.[14] Pycnidia are approximately 0.3 mm in diameter, yielding conidia measuring 6–7 × ca 0.5 μm.[14] Chemical spot tests performed on the medulla (C–, K–, KC–, Pd–, UV–) consistently confirm the presence of usnic and evernic acids, as well as atranorin.[14] Distinguishing E. prunastri from similar species is crucial for accurate identification. It can be mistaken for Ramalina farinacea, which lacks the characteristic white underside, possesses narrower and more straggly branches, and exhibits distinctive oval soralia on its lobe edges. Similarly, Pseudevernia furfuracea can cause confusion, as it features a silver-grey upper side, often with isidia, and a lower surface that darkens to black in older sections.[6] Morphological variations within the species are also observed, with specimens from shaded habitats tending to develop fewer, paler, and more elongate lobes, while those from polluted sites often display reduced size, contorted forms, or eroded lobes.[14]
Lichens are increasingly understood not merely as a simple two-partner symbiosis but as complex ecosystems, a concept encapsulated by the "holobiont." This perspective recognizes that lichens host diverse microbial communities beyond the primary mycobiont and photobiont, including various non-lichenized fungi (often referred to as 'lichen-inhabiting fungi' or 'endolichenic fungi' (ELF)) and bacteria.[2] Studies have identified numerous lichenicolous fungi specifically associated with Evernia prunastri, providing a comprehensive list that includes Athelia arachnoidea, Briancoppinsia cytospora, Illosporiopsis christiansenii, Lichenoconium erodens, Lichenodiplis lecanorae, Lichenostigma maureri, Marchandiomyces corallinus, Phaeospora everniae, Phoma everniae, Spirographa spp. (including anamorphs Cornutispora ciliata and C. lichenicola), Unguiculariopsis lettaui, and unclassified species from the genera Abrothallus and Endococcus.[14] Furthermore, N. serpens has been specifically identified as an endolichenic fungus exhibiting high diversity within Evernia prunastri.[15] The presence of these associated microorganisms is well-documented, yet their precise lifestyles and interactions within the lichen thallus remain largely unexplored.[15] However, these microbial partners are recognized for their significant ecological roles and their potential for industrial applications, particularly as producers of novel secondary metabolites.[15] This multi-organismal composition suggests that the observed biological properties of E. prunastri, such as its antimicrobial, antioxidant, and anticancer activities, may not originate solely from the primary fungal or algal symbionts. Instead, these properties could be a synergistic product of the entire microbial community interacting within the thallus. This understanding adds a significant layer of complexity to the study of E. prunastri's chemistry and pharmacology, but simultaneously opens novel avenues for drug discovery. The associated microbes themselves are known to produce diverse bioactive secondary metabolites, implying that E. prunastri functions as a "microbial factory" for a wider range of compounds than previously attributed to the main symbionts alone. A comprehensive understanding of these complex interactions is crucial for fully harnessing E. prunastri's potential and for developing effective in vitro cultivation strategies that can replicate the natural environment to ensure the production of desired, complex bioactive profiles.
Evernia prunastri exhibits a broad geographic distribution across mountainous temperate forests throughout the Northern Hemisphere, with documented presence in countries such as France, Portugal, Spain, various regions of North America, and a significant portion of Central Europe.[1] It is particularly widespread and often abundant throughout Britain and Ireland.[6] The primary substrate for its growth is the trunk and branches of oak trees, though it commonly colonizes the bark of other deciduous trees and conifers, including fir and pine.[9] This lichen demonstrates a wide ecological amplitude, thriving in well-lit, often exposed conditions. It preferentially grows on neutral to acid-barked trunks or twigs and is frequently observed in the canopy of wayside and parkland trees, as well as within hedgerows.[6] Less commonly, it can be found on fence-posts, old stems of Calluna, on the ground in heathland and dunes, or in more sheltered woodland and boggy sites.[14] Occasionally, E. prunastri also colonizes nutrient-rich siliceous rocks, gravestones, stabilized shingle, short turf, and brick walls.[14]
The species is highly sensitive to air pollution, particularly sulfur dioxide (SO2) and ammonia.[5] Historically, during the peak of SO2 pollution in Central Europe from the 1950s to the 1990s, its distribution significantly contracted, leading to a "total retreat" from heavily affected areas.[5] However, its reappearance in a region serves as a clear indicator of reduced SO2 levels, a trend observed in the English Midlands and urban areas since the 1980s following the implementation of Clean Air Acts.[6] While E. prunastri is now almost ubiquitous in these recovered regions, it remains sensitive to high levels of ammonia pollution.[14] Studies involving E. prunastri transplants have revealed that while the physiological status of the lichen itself may not undergo significant changes immediately after exposure, positive correlations exist between the diversity of epiphytic lichens at sampling sites and physiological parameters, such as photosynthetic pigments, in the transplants.[5] Furthermore, sites where E. prunastri naturally occurs tend to have a lower proportion of nitrophilous species, suggesting its capacity to recolonize urban environments with reduced air pollution and low eutrophication.[5]
Evernia prunastri is widely recognized and utilized for biomonitoring purposes, serving as both a bioindicator of air quality and a bioaccumulator of atmospheric deposition, especially heavy metals.[5] Fruticose species like E. prunastri are preferred for lichen transplant studies due to their larger biomass per thallus, ease of cleaning and installation, and enhanced sample homogeneity, which collectively streamline processing time.[16] It contributes a notable 18.3% of the bioaccumulation data in existing lichen transplant studies.[16] Research on metal desorption from E. prunastri using simulated acid rain solutions indicates that the mass percentage of desorbed metals is influenced by the strength of the bond between the metal and lichen tissue components, as well as the pH of the precipitation.[11] This observation suggests that E. prunastri, under certain environmental conditions, particularly those involving acidic precipitation, could potentially act as a secondary environmental pollutant by releasing accumulated metals.[11] This adds a critical layer of complexity to its environmental applications, moving beyond its passive role as a monitor to reveal its active participation in environmental biogeochemistry. Its capacity to release accumulated metals means it could contribute to secondary contamination, particularly in aquatic or soil systems downstream from polluted areas. Therefore, future biomonitoring studies should not only focus on the accumulation phase but also on the dynamics and reversibility of pollutant release, especially in regions experiencing fluctuating environmental conditions or acid rain. This comprehensive understanding is essential for accurate environmental risk assessment and management. The lichen demonstrates a very strong ability to adsorb ionic Cadmium (Cd), accumulating concentrations several orders of magnitude higher than those found in unpolluted thalli, thereby confirming its efficiency as a biomonitor for Cd availability.[17] The accumulation of ionic elements in lichens involves both intracellular and extracellular processes, with non-essential elements like Cd showing higher rates of extracellular accumulation.[17] While metal accumulation in lichens is a partially reversible process, some Cd release has been observed, particularly at higher concentrations, indicating the dynamic nature of pollutant uptake and release.[17] Future research is imperative to gather more bioaccumulation data for E. prunastri to refine and strengthen interpretative scales for biomonitoring. Optimizing exposure durations (with a general agreement for at least 6-8 weeks) and establishing adequate sample sizes for unexposed samples are also crucial for ensuring reliable and repeatable biomonitoring results.[16]
Evernia prunastri is recognized as a rich source of diverse bioactive secondary metabolites, which are compounds not directly involved in the organism's primary growth or development but play crucial roles in defense, signaling, or adaptation.[1] The chemical composition of E. prunastri extracts is predominantly characterized by depsides, phenolic acids, and dibenzofurans.[11] These secondary metabolites can constitute a significant portion of the lichen's dry weight, accounting for up to 5-20%.[18] Beyond these, the main compounds forming the cell walls and extracellular matrices of Evernia prunastri are glucans and galactomannans. These polysaccharides are notable for their gel and film-forming properties, coupled with good biocompatibility, safety, and biodegradability, making them attractive for various industrial applications.[13] The extracellular polymeric substances (EPS) are complex, believed to include polyuronic acids, glucans, heteropolysaccharides, pigments, phenolic compounds, lipids, and proteins, secreted by both the mycobiont and photobiont.[13]
Key compounds identified in Evernia prunastri include:
The chemical composition of E. prunastri extracts is highly dependent on the solvent used for extraction (e.g., ethyl-acetate, hexane, methanol, acetone, dichloromethane), which selectively isolates different classes of compounds and thus influences the spectrum of observed bioactive properties.[1] Total polyphenolic content also varies with the polarity of extracts, with lower polarity extracts generally being richer in these compounds.[11] Molecular docking studies have identified sekikaic acid as another promising compound, demonstrating strong binding affinities to catalytic sites for various enzyme inhibitions.[11] The primary structural components of the lichen's cell walls include glucans, galactomannans, and chitin.[13] This detailed information reveals that E. prunastri is not a singular source of bioactives; rather, its therapeutic and industrial potential is profoundly shaped by the precise engineering of the extraction process. Different solvents selectively isolate distinct classes of compounds (e.g., hydrophobic versus hydrophilic, specific depsides versus polysaccharides), leading to varied pharmacological outcomes. This implies that future research should move beyond generic extraction and focus on a systematic optimization of methods, potentially employing a combinatorial chemistry approach to extraction. This would allow for the precise targeting and maximization of specific desired bioactive compounds for particular applications, such as a potent anti-cancer compound versus a specific perfumery fixative. Consequently, comparisons of bioactivity across different studies must rigorously account for and report the specific extraction solvent and methodology used to ensure scientific validity and reproducibility.
| Compound Name | Chemical Class | Key Biological Activities | Relevant Source |
|---|---|---|---|
| Evernic Acid (EA) | Depside | Antioxidant, Anti-inflammatory, Antimicrobial (potential new antibiotic class), Neuroprotective (AChE, BChE, Tyrosinase inhibition), Hypoglycemic (α-glucosidase inhibition) | [4] |
| Atranorin (ATR) | Depside | Antioxidant, Anti-inflammatory, Neuroprotective (AChE, BChE, Tyrosinase inhibition), Hypoglycemic (α-glucosidase inhibition) | [4] |
| Usnic Acid | Dibenzofuran | Antioxidant (free radical scavenging, lipid peroxidation inhibition, metal chelation), Antimicrobial (Gram-positive bacteria, mycobacteria), Antiviral, Anti-inflammatory | [4] |
| Glucans | Polysaccharide | Gel-forming, Film-forming, Wound Healing (enhances macrophage infiltration, tissue granulation, collagen deposition, reepithelialization) | [13] |
| Galactomannans | Polysaccharide | Gel-forming, Film-forming | [13] |
| Orsellinic Acid | Phenolic Acid | Chemical constituent | [11] |
| Rosmarinic Acid | Phenylpropanoid / Phenolic Acid | Antioxidant, Anti-inflammatory, Anticancer | [19] |
| Caffeic Acid | Phenylpropanoid / Phenolic Acid | Antioxidant, Anti-inflammatory, Anticancer | [19] |
| Trans-Cinnamic Acid | Phenylpropanoid / Phenolic Acid | Antioxidant, Anti-inflammatory, Anticancer | [19] |
| Chlorogenic Acid | Phenolic Acid | Antioxidant, Anti-inflammatory, Anticancer | [19] |
| Sekikaic Acid | Depside | Enzyme inhibition (molecular docking) | [11] |
| Emodin Anthrone | Anthraquinone | Cytotoxic (potential for hyperproliferative skin diseases like psoriasis) | [19] |
Evernia prunastri extracts exhibit significant antioxidant effects, which have been rigorously evaluated through multiple in vitro assays. These include free radical scavenging (DPPH and ABTS), reducing power (CUPRAC and FRAP), metal chelation, and phosphomolybdenum methods. These studies consistently demonstrate the lichen's strong potential for oxidative stress relief.[1] Specifically, the methanolic extract has shown a higher antioxidant potential compared to other extracts.[19] A strong correlation has been established between the antioxidant capacity of E. prunastri extracts and their total phenolic content, indicating that phenolic compounds are key contributors to this activity.[19] Key compounds like usnic acid and evernic acid play a significant role in antioxidant activity, offering protection against hydrogen peroxide-induced cytotoxic damage in central nervous system-like cells and modulating endogenous antioxidant enzymes such as superoxide dismutase (SOD) and catalase.[12] Usnic acid's ability to prevent lipid peroxidation has been noted as comparable to that of vitamin E.[12]
Both the polymeric and liquid phases of E. prunastri extracts have demonstrated high anti-inflammatory activity, notably through the inhibition of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) enzymes.[19] Aqueous and methanolic extracts have been shown to reduce human red blood cell (HRBC) hemolysis damage and moderately suppress protein denaturation, further reflecting their anti-inflammatory potential.[19] Specific compounds like evernic acid and atranorin have been identified as having inhibitory effects on COX-2.[4]
E. prunastri extracts consistently demonstrate significant antibacterial properties against a range of bacterial strains.[1] They are generally more effective against Gram-positive bacteria than Gram-negative bacteria.[3] Hexane and dichloromethane extracts have shown potent activity against Staphylococcus aureus, with minimum inhibitory concentrations (MICs) as low as 4 µg/ml for the dichloromethane extract.[12] An acetonitrile extract also exhibited activity against both S. aureus and Candida albicans.[19] Evernic acid has been specifically identified as an active antimicrobial compound, positioning it as a potential candidate for a new class of antibiotics.[19] Usnic acid, a well-known lichen metabolite, is already commercially used as an antibacterial ingredient in deodorants and toothpastes, effective against Gram-positive bacteria and mycobacteria.[12] It is important to note a discrepancy in the literature: while various solvent extracts show strong antimicrobial activity [23], the essential oil of E. prunastri has been reported to show only antifungal activity in one study, with minimal effect against Gram-negative bacteria and modest activity against Gram-positive bacteria.[3] This highlights the profound impact of extraction methods on the resulting bioactive profile.[23] This substantial discrepancy underscores a critical methodological challenge in natural product research: the significant influence of extraction methods on the resulting chemical profile and, consequently, the observed bioactivity. It suggests that generalizations about a species' pharmacological potential can be misleading without precise details on how the extract was prepared. This implies a strong need for the development and adoption of standardized protocols for both extraction and bioactivity testing to ensure reproducibility and comparability of results across different studies and laboratories. Furthermore, comprehensive chemical characterization of the exact composition of each specific extract tested is crucial for establishing clear structure-activity relationships and linking specific compounds to observed activities. Deeper investigation into the underlying mechanisms of action for both active and inactive extracts is also necessary to understand why certain preparations are effective while others are not. This contradiction serves as a pivotal learning point for designing future research in natural product pharmacology.
Methanolic extracts of E. prunastri have demonstrated strong anticancer effects, significantly reducing the growth of human cancer cell lines (HT-29, PC-3, and A549) by 62.96% to 75.56%, notably without cytotoxic effects on non-tumor cells.[19] Evernic acid, a key metabolite, suppressed proliferation in a dose-dependent manner and exhibited notable antimigratory ability on breast cancer MCF-7 and MDA-MB-453 cell lines. Its anticancer effect is mediated by inhibiting Thioredoxin reductase 1 (TrxR1) enzyme activity.[19] Emodin anthrone, another compound found in lichens, has shown high cytotoxicity to keratinocytes and fibroblasts, suggesting its potential in treating hyperproliferative skin diseases such as psoriasis.[19]
Extracts of E. prunastri have exhibited anti-cholinesterase and anti-tyrosinase activities, which are crucial in the context of neurodegenerative disorders like Alzheimer's and Parkinson's diseases.[1] Atranorin, a main compound, possesses a high capacity to inhibit acetylcholinesterase (AChE).[11] Molecular docking studies and in vitro tests have confirmed the inhibitory effects of evernic acid and atranorin on AChE, BChE, and tyrosinase, and their ability to penetrate the blood-brain barrier has also been confirmed, indicating their potential for central nervous system applications.[4]
E. prunastri extracts have shown significant in vitro enzyme inhibition activities relevant to diabetes management, specifically targeting anti-amylase and anti-glucosidase.[1] Hexane extracts, in particular, demonstrated high α-glucosidase inhibition rates, ranging from 80.69% to 94.18%.[11] The efficacy of E. prunastri extracts in α-glucosidase inhibition was comparable to that of acarbose, a positive control, even at ten-times-lower concentrations, highlighting its strong potential as an antidiabetic agent for blood sugar control.[11]
Beyond these primary activities, historical and preliminary research suggests broader biological activities including antipyretic, cytotoxic, anti-inflammatory, antitumor, and analgesic effects.[3] Anti-hyaluronidase activity has also been demonstrated.[11] Most E. prunastri extracts have shown a positive effect on cell viability, suggesting their potential for inclusion in dermatological products.[19] The presence of beta-glucans in E. prunastri suggests potential for wound healing applications, as these compounds are known to enhance wound repair processes.[19] In a modern context, Evernia prunastri extract is utilized in allergy testing as an allergenic extract, notably in patch tests like the T.R.U.E. Test, at a dosage of 81 ug/48h.[26] The diverse biological activities of E. prunastri extracts and its main compounds (evernic acid, atranorin) are often described as "pleiotropic properties," meaning these compounds simultaneously exhibit multiple pharmacological actions, such as antioxidant, anti-inflammatory, neuroprotective, antidiabetic, antimicrobial, and anticancer effects.[4] In contemporary drug discovery, single-target drugs often face limitations such as the development of resistance or insufficient efficacy for complex, multifactorial diseases. Pleiotropic compounds, by modulating multiple pathways or targets concurrently, could offer more robust and effective therapeutic strategies for conditions like diabetes, neurodegenerative disorders, or certain cancers.[1] This suggests a potential shift from the traditional "one drug, one target" approach to developing multi-faceted therapies derived from natural sources like E. prunastri. This also has significant implications for the functional food industry, where a single ingredient could provide a broad spectrum of health benefits.
| Type of Extract | Target Organism/Enzyme | Reported Efficacy Metric | Value (with units) | Relevant Source |
|---|---|---|---|---|
| Ethyl-acetate (EtOAc) | α-amylase | % Inhibition | Significant | [1] |
| Ethyl-acetate (EtOAc) | α-glucosidase | % Inhibition | Significant | [1] |
| Hexane | α-glucosidase | % Inhibition | 80.69% (at 3 mg/mL), 94.18% (at 5 mg/mL) | [11] |
| Ethyl-acetate (EtOAc) | Cholinesterase | % Inhibition | Significant | [1] |
| Ethyl-acetate (EtOAc) | Tyrosinase | % Inhibition | Significant | [1] |
| Methanolic | HT-29 (human cancer cell line) | % Growth Reduction | 67.03% | [19] |
| Methanolic | PC-3 (human cancer cell line) | % Growth Reduction | 75.56% | [19] |
| Methanolic | A549 (human cancer cell line) | % Growth Reduction | 62.96% | [19] |
| Methanolic | HT-29 (human cancer cell line) | IC50 | 100 ± 0.04 μg/mL | [19] |
| Methanolic | PC-3 (human cancer cell line) | IC50 | 146 ± 0.05 μg/mL | [19] |
| Methanolic | A549 (human cancer cell line) | IC50 | 112 ± 0.06 μg/mL | [19] |
| Dichloromethane (DCM) | Staphylococcus aureus | MIC | 4 µg/mL | [12] |
| Hexane | Staphylococcus aureus | MIC | 21 µg/mL | [12] |
| Acetonitrile (ACN) | Staphylococcus aureus | MIC | 14 µg/mL | [19] |
| Acetonitrile (ACN) | Candida albicans | MIC | 38 µg/mL | [19] |
| Methanolic | Staphylococcus aureus isolates | MIC | 0.07 to 0.15 mg/mL | [12] |
| Acetone-methanolic | Staphylococcus aureus, MRSA | MIC | 0.03125 mg/mL | [23] |
| Acetone-methanolic | E. coli, P. aeruginosa | MIC | 0.5 mg/mL | [23] |
| E. prunastri extract (unspecified) | Elastase | % Inhibition | Highly effective | [19] |
| E. prunastri extract (unspecified) | COX-1, COX-2 | % Inhibition | High | [19] |
| Essential Oil | Gram-negative bacteria | Effect | Little effect | [3] |
| Essential Oil | Gram-positive bacteria | Effect | Modest antibacterial activity | [3] |
| Essential Oil | Staphylococcus aureus | Inhibition Zone | 7-9 mm (low effect) | [3] |
| Essential Oil | Staphylococcus epidermidis | Inhibition Zone | 7-9 mm (low effect) | [3] |
| Essential Oil | Fungi | Activity | Antifungal activity | [24] |
Evernia prunastri, commonly known as oakmoss, is an edible lichen.[1] Historically, it was notably used by ancient Egyptians for making bread, indicating its long-standing role as a functional food source.[1] Archaeological findings, such as baskets filled with oakmoss discovered in ancient Egyptian royal tombs, suggest its historical importance, although its definitive purpose—whether for perfume or food—in these contexts is not entirely clear.[8]
In the perfumery industry, oakmoss is highly valued for its distinctive heavy, oriental fragrance and its exceptional properties as a fixative base, which helps prolong the scent of other fragrance components.[8] Its use in perfumery dates back to at least the 16th century.[8] It forms a foundational component of the Fougère and Chypre fragrance families.[9] The lichen's natural odor is complex, described as woody, sharp, and slightly sweet.[9] A unique characteristic is the pronounced turpentine odor of oakmoss growing on pines, which is specifically valued in certain perfume compositions.[9] Its fragrant compounds are commercially extracted as "oakmoss absolutes and extracts," primarily in the Grasse region of France, a renowned center for perfumery.[9]
In traditional medicine systems, E. prunastri has been used for a variety of ailments, including jaundice, pulmonary conditions, stomach issues, and cranial diseases.[3] Historically, a mixture of acids extracted from oakmoss was employed in drugs for treating external wounds and infections.[8] It was also applied externally as a disinfectant, to stop bleeding, and for treating various skin infections and sores, including those in the mouth.[22] In modern medicine, Evernia prunastri extract is specifically utilized as an allergenic extract in allergy testing. It is a component of patch tests, such as the T.R.U.E. Test, with a typical dosage of 81 ug/48h.[26] Beyond allergy testing, there is significant potential for its topical applications in dermatology and skincare, driven by its demonstrated anti-inflammatory, depigmentation (anti-tyrosinase), and wound healing properties.[19] Usnic acid, a key metabolite, is already incorporated into deodorants and toothpastes for its antibacterial action.[19]
Other industrial and cultural uses include its historical application in the production of natural colors and alcohol.[3] Given its broad spectrum of biological activities, E. prunastri holds significant potential for further development as a functional food ingredient.[1] Research indicates its utility in the formulation of antimicrobial bio-based films, leveraging its bioactive compounds and biopolymers.[18] A notable innovation involves the valorization of residual solid biomass, remaining after extraction processes, into high-value artificial humic substances (AHSs).[13] These AHSs mimic natural humic substances found in soil and have potential applications in agriculture, such as enhancing nutrient availability, and in environmental remediation, for instance, by removing heavy metals from wastewaters.[13] The evolution of Evernia prunastri's utility from traditional, empirical applications to modern, scientifically validated and diversified uses underscores the enduring value of ethnobotanical knowledge. Its historical uses, such as for bread-making by ancient Egyptians and in traditional folk medicine, provided an empirical foundation that modern scientific inquiry has now begun to validate and expand upon. This progression from traditional practices to sophisticated biotechnological applications highlights how ancient wisdom can guide contemporary research, leading to the discovery of new therapeutic and industrial potentials for natural resources. The continuous re-evaluation and scientific validation of traditional uses not only preserves cultural heritage but also accelerates the pace of drug discovery and sustainable product development, demonstrating a powerful synergy between past knowledge and future innovation.
The commercial interest in lichens, including Evernia prunastri, has been significantly constrained by their inherently slow growth rate and the considerable difficulties associated with their cultivation in laboratory settings.[18] Evernia prunastri grows slowly on trees in temperate woodlands, and its manual harvesting is a time-consuming and labor-intensive process.[27] For biodiversity conservation, sustainable forest management practices must acknowledge that not all lichen species are tolerant of intensive harvesting. Therefore, low-intensity harvesting methods are crucial to allow for their natural regeneration.[18]
The sustainability of oakmoss extract production faces several critical challenges. Its slow growth and limited geographic distribution, primarily in specific regions of Europe and North America, restrict its natural availability.[27] The labor-intensive nature of manual picking further contributes to the high cost of oakmoss extract.[27] Moreover, Evernia prunastri is highly susceptible to pollution and other environmental disturbances, making sustainable sourcing particularly difficult.[27] While it is a renewable resource, the considerable time required for its regrowth after harvesting poses a significant challenge for meeting commercial demand sustainably.[27] The species is listed as critically endangered (CR) in Iceland, where it is found in only one location, highlighting regional conservation concerns.[9]
To address these challenges, substantial efforts are being directed towards developing green extraction methods and innovative biorefinery approaches. Conventional solvent extraction techniques, while common, often involve aggressive chemicals, are time- and energy-consuming, and can lead to polysaccharide degradation.[13] Consequently, there is an increasing demand for greener alternatives that prioritize safety and environmental considerations.[18] Notable advancements include the use of non-toxic ionic liquids and natural deep eutectic solvents (NaDES).[18] Microwave-assisted hydrothermal processing, either as a standalone method or combined with supercritical CO2 extraction, has been proposed for the sequential extraction of bioactives and biopolymer fractions.[13] The environmental assessment using the EcoScale has indicated that NaDES microwave extraction is the most sustainable option among tested processes, attributed to its low toxicity, rapid heating time, and good yield of polysaccharides.[13] This integrated extraction/formulation process has demonstrated a reduction in energy consumption by 35% and production time by 23% compared to traditional polysaccharide formulation methods.[13] The valorization of residual solid biomass, often discarded or combusted from waste forestal biomass and low-value tree fractions, into high-value artificial humic substances (AHSs) represents a promising biorefinery approach.[13] This implementation of an extraction stage as an initial step in lignocellulosic biorefineries could significantly enhance the economic viability of the overall process by yielding high-value-added products.[18] This demonstrates a strategic shift towards circular economy principles, where every component of the biomass is utilized, thereby reducing waste and maximizing resource efficiency.
The diverse biological properties of Evernia prunastri extracts, particularly their anti-inflammatory, anticancer, antioxidant, and antimicrobial activities, position the lichen as a promising candidate for various emerging applications and drug discovery initiatives.[19] The demonstrated efficacy of methanolic extracts against human cancer cell lines (HT-29, PC-3, A549) without cytotoxicity to non-tumor cells, along with the identification of evernic acid as an active antimicrobial agent, highlights its significant therapeutic potential.[19] Furthermore, the neuroprotective effects of evernic acid, offering protection against oxidative stress-induced damage in central nervous system cells, suggest its relevance in treating neurodegenerative disorders.[19]
Beyond internal consumption, E. prunastri holds considerable promise for topical applications. Its extracts have shown potential for elastase inhibition, which is relevant for anti-aging and skin elasticity, and anti-tyrosinase activity, indicating depigmentation potential for skin-whitening products.[19] The presence of beta-glucans also suggests utility in wound healing, as these compounds are known to enhance wound repair processes.[19] While these findings are promising, further studies are required to confirm the safety and efficacy of these compounds for human topical applications.[19]
Several unresolved questions and areas for future research warrant attention to fully unlock the potential of Evernia prunastri:
Evernia prunastri, commonly known as Oakmoss, is a remarkable lichen species with profound ecological significance and extensive biotechnological potential. Its unique biological characteristics, including its classification as a fruticose lichen with distinct morphological features and its role as a complex holobiont hosting diverse microbial communities, underscore its adaptability and rich biological profile. The species serves as a critical bioindicator of air quality, demonstrating acute sensitivity to pollutants like sulfur dioxide and ammonia, with its return to urban areas signaling environmental recovery. However, its capacity to desorb accumulated heavy metals under certain conditions also highlights a complex environmental dynamic that warrants further investigation.
Chemically, E. prunastri is a prolific producer of a wide array of bioactive secondary metabolites, notably depsides like evernic acid and atranorin, and dibenzofurans such as usnic acid. These compounds, along with various phenolic acids and polysaccharides, contribute to the lichen's diverse pharmacological activities. The demonstrated pleiotropic properties of its extracts, encompassing antioxidant, anti-inflammatory, antimicrobial, anticancer, neuroprotective, and antidiabetic effects, suggest a promising paradigm for multi-target therapeutic development against complex diseases. However, the variability in reported bioactivities based on extraction methods emphasizes the critical need for standardized protocols and comprehensive chemical characterization in future research.
Historically valued in perfumery for its unique fragrance and as a fixative, and traditionally used as an edible component and in folk medicine, Evernia prunastri continues to find modern applications in allergy testing and topical dermatological formulations. The challenges associated with its slow growth and sustainable harvesting necessitate the development of advanced cultivation techniques and green extraction methods, such as those employing natural deep eutectic solvents within a biorefinery framework.
Looking forward, research into Evernia prunastri should prioritize refining biomonitoring methodologies, deepening the understanding of its complex microbial interactions within the holobiont, and exploring its potential for active environmental remediation. Advances in controlled cultivation and extraction technologies are essential to sustainably harness its rich chemical diversity for pharmaceutical, cosmetic, and functional food industries. The enduring value of Evernia prunastri, from ancient uses to cutting-edge scientific inquiry, positions it as a vital organism for both ecological health and human well-being, with its full potential still unfolding through dedicated research.
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Evernia divaricata - Mountain oakmoss [E-flora] Evernia mesomorpha - Boreal oakmoss [E-flora] |
Evernia perfragilis - Arctic oakmoss [E-flora] Evernia prunastri - Valley oakmoss [E-flora] |