Usnea (Usnea barbata)

Usnea barbata is a fruticose lichen formed by a symbiosis between a fungus and a green alga. It typically appears as a hanging, filamentous mass with a branched, hair-like structure, often described as “beard-like.” The thallus is usually grey-green to yellowish-green, with thin, elastic branches that can reach several centimetres in length. When gently stretched, the outer cortex may break, revealing a characteristic white, elastic central cord, a useful macroscopic feature for recognising the genus Usnea.

This lichen grows mainly on the bark of trees, both conifers and broadleaves, in cool, humid environments with good air circulation. It is particularly frequent in forests with low levels of atmospheric pollution, and for this reason it is often considered a useful bioindicator of air quality. The growth rate of Usnea barbata is generally slow, and the development of noticeable tufts indicates stable ecological conditions over time. It does not feed on the host tree: it is an epiphyte, anchored to the bark but obtaining water and nutrients directly from rain, fog and airborne particles.

From a structural point of view, Usnea barbata shows a typical lichen organisation with an outer cortex, an algal layer, a medulla and the central cord. The surface can be finely papillose or slightly rough, and the branching pattern is often more or less dichotomous. The lichen can host various secondary metabolites, among which usnic acid is one of the most characteristic. This compound, together with other lichen substances, contributes to the typical colour and influences some of the biological properties associated with the species.

Ecologically, Usnea barbata participates in nutrient cycles by intercepting particles from the atmosphere and slowly releasing them to the ecosystem through decomposition. Its presence is associated with well-preserved forest habitats and relatively stable microclimatic conditions, making it of interest in ecological monitoring and environmental assessment.

Botanical classification
Common name: old man’s beard / beard lichen
Clade: Ascomycota
Order: Lecanorales
Family: Parmeliaceae
Genus: Usnea
Species: Usnea barbata (L.) F.H.Wigg.

Cultivation and growth conditions

Climate
Usnea barbata is typical of temperate and cold regions, characterized by clean air, high atmospheric humidity and moderate temperature ranges. It grows in forests, valleys and mountainous areas with little or no air pollution. It tolerates frost, long periods of moisture and low direct radiation, while it suffers in environments that are excessively hot, dry or contaminated by pollutants.

Exposure
The species prefers shaded or semi-shaded positions, such as woodland with diffuse light. Excessive, direct solar radiation can induce desiccation of the thallus, whereas moderate, constant light combined with sufficient humidity supports regular growth.

Soil
Usnea barbata does not use the soil as a source of nutrients. It attaches to bark of conifers and broadleaves, to rocks or dead wood. Soil properties act indirectly, through their effect on the host vegetation. Healthy trunks with bark that is neither too smooth nor heavily treated (e.g. with chemicals) favour thallus attachment and development.

Irrigation
No artificial irrigation is required. Water supply comes from the atmosphere (rain, fog, dew). High air humidity is fundamental for metabolic activity; very dry air causes thallus dehydration and slows growth. Natural cycles of wetting and drying form part of the normal physiology of lichens.

Temperature
The species tolerates low temperatures and prolonged cold periods. Optimal conditions fall within a broad range, roughly 4–18 °C. Persistent heat, low humidity and air pollution reduce the photosynthetic efficiency of the algal partner within the lichen and limit growth.

Fertilization
No fertilization is needed. As with other lichens, essential nutrients are obtained from the air, from precipitation and from slow mineralization of suspended particles deposited on the thallus. Direct nutrient inputs or fertilizers are unnecessary and may even alter the delicate physiological balance of the symbiosis.

Crop care
True “cultivation” is difficult, since the species depends on very specific environmental conditions. Management is essentially limited to preserving intact habitats, with clean air, high humidity and undamaged host vegetation. Natural lichen communities do not require direct interventions; in human-impacted areas, conservation of woodland and reduction of atmospheric pollution are the main protective measures.

Harvesting
Traditional harvesting consists of collecting mature thalli from their substrates, taking care not to damage the bark of the host and leaving part of the material in place to allow regeneration. The harvested thalli are cleaned of wood fragments and debris, then dried in a shaded, well-ventilated area. Because growth is slow, harvesting should be moderate and sustainable.

Propagation
Propagation occurs mainly by fragmentation of the thallus: small pieces detached by wind, snow or mechanical movement can be transported to new substrates, where they re-attach and regenerate a new lichen individual. Sexual reproduction via spores is also possible but requires stable environmental conditions, constant humidity and long time spans. For controlled colonization, small thallus fragments can be placed on healthy, untreated bark in humid, shaded sites and left to adhere and grow gradually over several years.

Indicative nutritional values per 100 g

(dried material – approximate)

• Energy: ~ 200–260 kcal

• Water: ~ 6–10 g

• Total carbohydrates: ~ 30–45 g (mostly structural polysaccharides)

• Dietary fibre: high

• Protein: ~ 7–12 g

• Total fat: ~ 2–4 g

• Minerals: calcium, magnesium, iron, zinc, copper, manganese

• Vitamins: traces of antioxidant compounds and water-soluble micronutrients

Values are indicative and strongly influenced by habitat, host tree, and environmental conditions.

Key constituents

• Lichen acids: usnic acid (major component), protocetraric acid

• Structural polysaccharides and fibre

• Polyphenols

• Triterpenes

• Trace minerals (Ca, Mg, Fe, Zn, Mn)

• Trace amounts of essential oil components and natural volatiles

Production process

(for dried crude drug, powders, extracts)

1. Harvesting

   • manual collection in clean forest areas

   • selection of intact, uncontaminated thalli

2. Cleaning

   • removal of bark fragments, needles, and wood particles

   • discarding dark, degraded, or mouldy material

3. Drying

   • slow drying in shaded, ventilated conditions

   • moderate temperatures to preserve usnic acid and other lichen acids

4. Fragmentation and cutting

   • tea-cut for herbal use or milling to obtain herbal powders

5. Optional extraction

   • hydroalcoholic or hot-water extraction

   • filtration and concentration for standardized extracts

6. Storage and packaging

   • dry, cool, dark conditions

   • airtight packaging to protect from moisture and oxidation

Physical properties

• filamentous, elastic, branched thallus

• pale grey-green colour

• compact, slightly rubbery texture

• pronounced hygroscopic behaviour

• typical fruticose lichen aspect (hair- or beard-like tufts)

Sensory and technological properties

• mild woodland, slightly resinous aroma

• herbal, slightly bitter taste

• infusion colour: pale yellow to yellow-green

• high water retention capacity of the lichen fragments

• suitable for low-dose inclusion in herbal blends

Food applications

(very restricted and essentially herbal)

• component of herbal tea blends in very small amounts

• traditional herbal infusions based on dried lichen

• occasional use in complex phytobotanical preparations

Note: It is not used as a conventional food; use as a household ingredient without expertise is discouraged.

Nutrition and health

The technical and scientific interest focuses mainly on lichen acids, especially usnic acid, as well as polyphenolic fractions and structural fibre. Polysaccharides contribute to the nutritional profile of the dried material, and minerals support cellular and enzymatic functions.

Modern use is essentially herbal, in controlled and dosed preparations. Duration and dosage should follow recognized technical guidelines and professional recommendations.

Portion note

There is no traditional “food portion”.
In herbal tea practice, approximately 1 g of dried Usnea barbata per cup is sometimes used, unless different professional instructions are given.

Allergens and intolerances

• not classified as a typical food allergen

• possible individual sensitivity to polyphenols or usnic acid

• prolonged or high-dose use without professional guidance is not recommended

• in topical use, may cause irritation in individuals with very sensitive skin

Storage and shelf-life

• store in cool, dry, dark conditions

• avoid direct light exposure

• close containers carefully after opening

• typical shelf-life: about 12–30 months under suitable conditions

Safety and regulatory aspects

• not considered a common food

• use restricted to herbal and phytoderived preparations

• presence of usnic acid requires caution: industrial formulations must declare standardization and technical limits where applicable

• compliance with regulations on purity, contaminants, drying processes, traceability, and proper labelling

• doses and uses in food supplements must follow applicable regulations and safety evaluations

Labelling

For approved herbal products, labels should state:

• name: Usnea / Usnea barbata

• plant part used (thallus)

• country/area of origin

• batch number and expiry or best-before date

• directions for use

• warnings

• any stated standardization in usnic acid or other lichen acids

Troubleshooting

In infusion

• weak aroma → slightly increase maceration time (keeping dose controlled)

• too bitter taste → reduce the amount or blend with milder herbs

• poor clarity → filter through fine mesh or paper filter

In storage

• earthy or musty odour → sign of residual or absorbed moisture

• marked discolouration → likely due to light exposure or prolonged storage

Main INCI functions (cosmetics)

Usnea barbata Extract may be used as:

• skin conditioning component

• botanical functional ingredient in “natural concept” products

• plant-identity ingredient in herbal-inspired cosmetic lines

Conclusion

Usnea barbata is a fruticose lichen with a distinctive filamentous, “beard-like” appearance and a strong connection to forest ecosystems. Its content of usnic acid, polyphenols, structural fibre, and minerals gives it a technically interesting profile for herbal and cosmetic applications.

Although it is not a direct food ingredient, it can be used in carefully dosed herbal infusions and plant-based formulations, always within the limits defined by regulations and good practice. When harvested responsibly and stored under proper conditions, it represents a light, discreet botanical material consistent with European phytotherapeutic tradition.

Mini-glossary

Usnic acid – major lichen acid in Usnea species, with marked bioactivity; requires careful control of dose and exposure.
Polyphenols – antioxidant plant compounds that contribute to chemical stability and potential biological effects.
Skin conditioning – cosmetic function that improves skin softness, comfort, and surface balance.

Studies

Among its components, the usnic acid, a component that can also induce toxicity (1), is used in supplements for weight loss, dandruff and more.

The aqueous methanolic extract of Usnea barbata has been successfully used as an antibiotic therapeutic agent against infections caused by Lactococcus garvieae on rainbow trout (2).

The extract has demonstrated antifungal properties at concentrations of 10mg ml^-1 against Alternaria alternaria, a parasite ascomycetes fungus that attacks the leaves and damages the crops of about 350 plant species and can induce allergies in humans (3).

Usnea barbata studies

References_________________________________

(1) Chen S, Zhang Z, Qing T, Ren Z, Yu D, Couch L, Ning B, Mei N, Shi L, Tolleson WH, Guo L. Activation of the Nrf2 signaling pathway in usnic acid-induced toxicity in HepG2 cells  Arch Toxicol. 2017 Mar;91(3):1293-1307. doi: 10.1007/s00204-016-1775-y.

Abstract. Many usnic acid-containing dietary supplements have been marketed as weight loss agents, although severe hepatotoxicity and acute liver failure have been associated with their overuse. Our previous mechanistic studies revealed that autophagy, disturbance of calcium homeostasis, and ER stress are involved in usnic acid-induced toxicity. In this study, we investigated the role of oxidative stress and the Nrf2 signaling pathway in usnic acid-induced toxicity in HepG2 cells. We found that a 24-h treatment with usnic acid caused DNA damage and S-phase cell cycle arrest in a concentration-dependent manner. Usnic acid also triggered oxidative stress as demonstrated by increased reactive oxygen species generation and glutathione depletion. Short-term treatment (6 h) with usnic acid significantly increased the protein level for Nrf2 (nuclear factor erythroid 2-related factor 2), promoted Nrf2 translocation to the nucleus, up-regulated antioxidant response element (ARE)-luciferase reporter activity, and induced the expression of Nrf2-regulated targets, including glutathione reductase, glutathione S-transferase, and NAD(P)H quinone oxidoreductase-1 (NQO1). Furthermore, knockdown of Nrf2 with shRNA potentiated usnic acid-induced DNA damage and cytotoxicity. Taken together, our results show that usnic acid causes cell cycle dysregulation, DNA damage, and oxidative stress and that the Nrf2 signaling pathway is activated in usnic acid-induced cytotoxicity.

Chen S, Dobrovolsky VN, Liu F, Wu Y, Zhang Z, Mei N, Guo L. The role of autophagy in usnic acid-induced toxicity in hepatic cells  Toxicol Sci. 2014 Nov;142(1):33-44. doi: 10.1093/toxsci/kfu154.

(2) Bilen S, Sirtiyah AMA, Terzi E. Therapeutic effects of beard lichen, Usnea barbata extract against Lactococcus garvieae infection in rainbow trout (Oncorhynchus mykiss). Fish Shellfish Immunol. 2019 Apr;87:401-409. doi: 10.1016/j.fsi.2019.01.046. 

(3)  AJ Afolayan, DS Grierson, L Kambizi, I Madamombe and PJ Masika In vitro antifungal activity of some South African medicinal plants  South African Journal of Botany 2002, 68: 72–76

Abstract. The acetone extracts of 12 plants used in folkloric medicine in the Eastern Cape of South Africa, were investigated for their in vitro antimycotic activity against five fungi using the agar dilution method. The extracts showed significant inhibition of growth of the test organisms at varying concentrations. Extracts from Arctotis arctotoides showed the highest activity at concentrations varying from 0.1 to 10mg ml− 1, followed by Usnea barbata, a lichen, while Grewia occidentalis demonstrated the least activity. Extracts from A. arctotoides, U. barbata, Combretum caffrum, Aloe ferox, Salix capensis, Schotia latifolia and Prunus persica were fungicidal at 10mg ml− 1 which was the highest concentration tested. The fungi differed significantly in their susceptibility to plant extracts with Alternaria alternaria, and Mucor hiemalis, being completely inhibited at 5 and 10mg ml− 1 by most of the extracts.

Guo L, Shi Q, Fang JL, Mei N, Ali AA, Lewis SM, Leakey JE, Frankos VH. Review of usnic acid and Usnea barbata toxicity. J Environ Sci Health C Environ Carcinog Ecotoxicol Rev. 2008 Oct-Dec;26(4):317-38. doi: 10.1080/10590500802533392. 

Abstract. Usnic acid is a prominent secondary lichen metabolite that has been used for various purposes worldwide. Crude extracts of usnic acid or pure usnic acid have been marketed in the United States as dietary supplements to aid in weight loss. The US Food and Drug Administration (FDA) received 21 reports of liver toxicity related to the ingestion of dietary supplements that contain usnic acid. This prompted the FDA to issue a warning about one such supplement, LipoKinetix, in 2001 (http://www.cfsan.fda.gov/~dms/ds-lipo.html). Subsequently, usnic acid and Usnea barbata lichen were nominated by the National Toxicology Program (NTP) for toxicity evaluations. At present, a toxicological evaluation of usnic acid is being conducted by the NTP. This review focuses on the recent findings of usnic acid-induced toxicities and their underlying mechanisms of action.