Lichens and People - Uses, Benefits and Potential Dangers
Lichens are fascinating organisms that are an important part of nature and are also useful for humans. Lichens provide us with dyes, food and scents for perfumes and deodorants. In the future, they may also provide us with antibiotics and sunscreen chemicals.
Lichens are either sensitive or resistant to pollution, depending on the species, and can withstand high levels of radiation. They can be used as biological sensors and give us information about their present or past environment.
Despite their appearance, lichens (pronounced "likens") aren't plants. Their bodies consist of both a fungus and an alga. Each organism helps the other in some way, creating a beneficial partnership.
Lichens have a variety of shapes. Some have a leafy appearance. Others have a highly branched form and look like little shrubs. Still others resemble thin crusts attached to surfaces. Lichens have many possible colors, including black, grey, white, green, blue-grey, yellow, orange, red or brown.
I live in the Pacific Northwest region of North America. Here lichens provide color and interest on my nature walks all year round. Even when deciduous plants are dormant, lichens, fungi, mosses and evergreen plants are a joy to see.
Lichens in a Seattle Cemetery
What are Lichens?
Lichens are beautiful and somewhat mysterious organisms that are classified into three main types, based on the form of their body, or thallus.
- Foliose lichens have a leaf-like appearance.
- Fruticose lichens have a highly branched form. They may be erect or hanging.
- Crustose lichens look like a crust that has formed on a surface.
Intermediate and unusual forms of lichens exist. For example, scaly lichens look like a cross between a crustose form and a foliose form. Jelly lichens live in moist areas and have a gelatinous appearance when wet.
Unlike a plant, a lichen doesn't have roots, stems or leaves. It's attached to its substrate by filaments called rhizines or by a single, central extension of the thallus called a holdfast. The rhizines and holdfast don't absorb water or nutrients from the substrate. Instead, the thallus absorbs the water and nutrients that it needs from the surrounding air and from raindrops.
Lichens grow on many different substrates, including wood, bark, rock, soil, concrete, metal, glass, plastic, cloth and leather. They even grow on the shells of living animals and on other lichens. They are also found in many different habitats, including temperate and tropical rainforests, deserts, mountains, the tundra, snowy and icy areas and seashores.
Lichens perform useful functions in nature. They provide shelter for other organisms. They also provide food for animals and materials that they can use to build their homes or nests. Lichens growing on rocks contribute to the slow process of rock breakdown and soil formation.
Symbiosis in Lichens
A lichen is an example of symbiosis - a relationship in which two organisms live in a close association. The alga in the lichen partnership may be a green alga or an organism that used to be called a blue green alga but is now known as a cyanobacterium. The fungus nearly always belongs to a group known as the ascomycetes.
Like most other fungi, the fungal component of a lichen consists of branching, thread-like structures called hyphae. The algal cells are generally located in the middle of the lichen, covered on the top and bottom and surrounded by hyphae. In jelly lichens the fungal hyphae and algal cells are mixed uniformly.
The algal cells make food for both themselves and the fungus. They contain chlorophyll, which absorbs sunlight. The alga uses the light energy to make food (carbohydrate) from carbon dioxide and water. Occasionally there are two kinds of algae in a lichen. Fungi don't contain chlorophyll and can't produce their own food. The fungus in a lichen helps the alga by protecting it.
Obtaining Dyes from Lichens
Historical methods of making dyes from lichens
Dyes and Pigments From Lichens
Lichens are often a grey color when they're dry. When a lichen is moistened and absorbs water, however, the algal cells give it a deeper hue. The fungus component is often colourless, but in some cases it contains a pigment that gives the lichen a vivid color.
Dyes for Wool and Silk
Making wool and fabric dyes from lichens is an ancient process. Suitable lichens are collected, cut into pieces and added to water. Often, ammonia is added to the water. At one time urine was commonly used as the water-ammonia solution. The mixture is left for several weeks in order for the dye to appear.
The dye made from a lichen often has a different color from the intact organism. Brown, gold, orange, green, purple, blue and red colors are all possible, depending on the species of lichen used and the type of extraction process.
Modern wool and fabric dyers often emphasize conservation as they collect lichens. They tend to gather lichens that have already become detached from their substrate or that are growing in a place from which they are likely to be removed, such as trees that have died. (Lichens don't harm trees.)
Litmus paper is very commonly used as an acid-base indicator, especially by students who don't need to know the exact pH of a substance. Litmus is a mixture of dyes extracted from specific lichens, especially Rosella tinctoria. Litmus paper is made from filter paper that has been treated with litmus. Neutral litmus paper is purple in color. It turns red when exposed to an acid and blue when exposed to a base (alkali).
Xanthoria parietina is a foliose lichen which contains a yellow pigment called parietin. This pigment absorbs ultraviolet radiation, acting as a sunscreen to protect the algal cells inside the lichen. Some other lichens contain sunscreens, too. It's been suggested that the protective chemicals could be useful in human sunscreens.
Usnic Acid as an Antibiotic
Antibiotics, Preservatives and Toxins from Lichens
Usnic acid has been found in several lichen species, including members of the Usnea genus. In natural medicine Usnea is used as an antibiotic and an anti-inflammatory substance. It's also used in some products as a preservative.
Tests in laboratory equipment and lab animals show that usnic acid has antimicrobial properties and kills bacteria, fungi and viruses. It also decreases inflammation and prevents some types of cancer cells from reproducing. Unfortunately, it may also cause serious liver damage. Clinical tests in humans are lacking.
The wolf lichen (Letharia vulpina) has a bright yellow-green color and grows in Europe and western North America. It contains a yellow chemical called vulpinic acid, which is poisonous to mammals. In the past, wolf lichen mixed with ground glass and meat was used as a poison for wolves. It's unknown if the lichen or the glass was most responsible for the death of the animals.
Wolf lichen has also been used for dye extraction and was once used medicinally by native peoples. Lab research shows that vulpinic acid can kill certain kinds of bacteria. As in the case of usnic acid, however, we need to find a way to prevent the chemical from hurting us before we can use it as an antibiotic.
Lichen Ingredients in Perfumes and Deodorants
Oakmoss (Evernia prunastri) is used to provide scents and fixatives for perfumes. It grows in Europe and North America but is especially valued in France. It lives on oak trees as well as other trees and is a fruticose lichen, not a moss.
Both essential oils and absolutes are extracted from the oakmoss. Essential oils are usually obtained by steam distillation. Absolutes are obtained by solvent extraction and are generally more concentrated than essential oils. The extracts of oakmoss are said to have a lovely earthy scent that resembles the aroma of moss and has an undertone of pine.
Some oakmoss extracts advertise the fact that they are low in atranol. This chemical is allergenic for some people, so its worthwhile seeking products that have little or no atranol.
Tree moss (Pseudevernia furfuracea) is another fruticose lichen used in the perfume industry. The lichen was used to fill the body cavity of Ancient Egyptian mummies. It's not known if the lichen was used as a preservative or to provide a pleasant scent. Today lichen components are used in deodorants as well as perfumes because of their pleasing aroma.
Lichens as Food
While we shouldn't pick up a lichen from a neighborhood rock or tree and eat it, some lichens are eaten by humans. Many lichens are mildly toxic, a few are poisonous and most are indigestible in their raw form. Some cultures have learned to prepare lichens in a way that improves their digestibility, however, and even makes them a delicacy.
Reindeer moss, or Cladonia rangiferina, is a fruticose lichen that is a staple food of reindeer and caribou. (This is yet another "moss" that is really a lichen.) Some Arctic inhabitants mix the partly digested lichen from caribou stomachs with raw fish eggs. The result is a concoction known as "stomach ice cream".
Umbilicaria esculenta is a black foliose lichen that grows on rocks. It's used in Asian cuisine after being fried. Umbilicaria lichens are often knows as "rock tripe". The North American version was used as an emergency food by early North American explorers.
Some lichens are boiled and mixed with fruit and flavoring agents such as onions before being eaten. With a few exceptions, lichens are generally used as food in famine situations instead of by choice, however.
A Lichen Survey in London, England
Lichens in Space
Lichens as Pollution and Environmental Indicators
Some lichens are very tolerant to pollutants such as nitrogen and sulfur compounds, while others are very sensitive to the presence of one or both of these chemicals. This enables people who can identify lichens to learn about local environmental conditions by observing which lichens are present. The lichens act as "bioindicators".
Lichens have a high resistance to damage by dehydration and the ability to quickly absorb a large quantity of water after dehydration ends. This property has enabled them to be used as wound dressings and diapers by people in the past. Lichens stop photosynthesizing when they dry out and start producing food again as they absorb water.
Lichens also absorb and store radioactive substances, such as cesium and strontium compounds, without apparent harm. Their thalli can be tested for the presence of radioactive compounds in order to learn about their environment.
At least some species of lichen are very resistant to dangerous radiation. In a 2005 experiment two species spent sixteen days in space inside an orbiting satellite. Here they were exposed to "massive" doses of ultraviolet and cosmic radiation. When they returned to Earth they had nearly the same photosynthetic ability as before the flight. In addition, most of the lichens' cells had no observable damage when examined under high magnification.
Hunting for Lichens
I love walking. Just about any walk that I take ends up as a nature walk. Looking for lichens and photographing them is an enjoyable part of my journey.
It's easy to find lichens where I live. They are sometimes very obvious, as in the photo above. Others may be overlooked by someone who doesn't pause to look at tree bark, twigs and rocks. The smaller parts of nature often live on these surfaces. It's fun to examine lichens and other creatures with or without a magnifying glass. It's also very interesting to think about the ways in which lichens are used by humans and the possible ways in which they may help us in the future.
© 2014 Linda Crampton
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