Lichens are some of the most amazing living things on this planet. Often the first form of life to colonise a new area of rock they occur all across the known world. Lichens are commonly seen and also commonly overlooked. Any structure that has been standing for a reasonable amount of time is likely to be adorned with lichens. Particularly, they are common on older buildings, stone walls, in graveyards and on most perennial (living more than 2 years) plants, particularly trees.

Lichens are inherently attractive, the more so the more you observe them. They are colourful - greens, greys, oranges and yellows are common colours. Cladonias often have bright red fruiting bodies adding to their attractiveness. The real beauty of lichens however is in their intricate shapes and often three dimensional forms. Lichens have very many shapes or forms and quite a number of these are like a delicate, intricately patterned filigree. Often lichens remind me of fine lace work, except that they are more colourful.

Lichens are amazing living entities, in that they are not a single organism like plants, animals or fungi. Instead every single lichen is the result of two or more separate organisms living permanently together. All lichens are made up of a fungal partner and either/or an algal partner or a cyanobacterium partner, or both (See What is a Lichen).

Lichens first appeared about 400 million years ago so they have been around for a long time. Some individual species such as Hypogymnia physodes have been around for at least 25 million years and maybe for as long as 70 million years. Obviously the lichen symbiosis is a successful strategy.

Lichens are scientifically fascinating, the symbiosis mentioned above is intriguing to many people and has been much studied, although it is not yet fully understood. Lichens are also of great use to ecologists.

Many lichens show a remarkable sensitivity to air quality. Some forms growing almost anywhere, others living in only the purist of atmospheres. For many ecologists lichens are an accurate monitor of quality of the air in any given place. You can do simple experiments on this with your class once you know how to identify a few species. Compare the diversity of lichens on similarly aged members of a given tree species, at home, at school, in the local park and in the nearby countryside. Once you have the basic equipment there is much that they amateur lichenologist can do. More on Lichens are pollution indicators.

Lichens are useful as food, medicine, for making dyes, in perfume manufacture, as decorations and in science. In Japan Umbilicaria esculenta is considered a delicacy where it is eaten as a soup or in salads. Other Umbilicaria species are, or have been, eaten in other countries. Some people believe that Lecanora esculenta was the original Biblical Manna as it has the habit of coming loose from its substrate (what it was growing on) and being blown around in the wind.

In the northern tundra Reindeer and Caribou eat loads of lichens, mostly species of Cladonia and Cetraria. Lichens can make up half the food these animals consume during the winter when they are dug up from below the snow by the hungry animals. Eskimos and Lapps both harvest and store these lichens as part of the winter feed for their animals.

Nutritionally, lichens contain practically no fat and only 1-5% protein. They are basically carbohydrate. Deer have a special enzyme called 'lichenase' which helps them to digest the lichens that they eat.

Medicinally Lichens have probably been used by many early civilisations. In Europe records from around the 15th century suggest that by then several lichens were in regular medicinal usage. For example, Usnea florida was used for hair problems, Xanthoria parietina for jaundice and Pettigera canina as a cure for rabies. In some northern places Cetraria islandica is still used as a cough remedy. On a more scientific basis, Usnic acid is a known antibiotic and has recently been developed into a salve in Germany. Research is still active into the use of several other lichen products as anti-viral and anti-fungal agents.

In Mediterranean countries red and purple dyes were long made from species of Roccella. Other purple dyes used in the 18th century were made from Pertusaria corallina in France and Ochrolechia tartarea in Scotland. A brown dye has also been manufactured from Parmelia omphalodes. Lichen dyes are still sometimes used for Harris Tweed, but the production of more modern dyes and ecological concerns over the amount of lichens harvested have pretty much rendered lichen dyes obsolete.

Lichens are still used in the perfume industry though. It is estimated that around 9,000 tonnes of lichens are used this way each year. Mostly this is made up of Evernia prunastri and Pseudevernia furfuracea. Lichens are also used as packaging materials by some florists and one study revealed that about 18,000 tonnes of Cladonia stellaris was exported from Finland to Germany and other European countries for this purpose.

Lichens are used by scientists not only in the study of the lichens' own life cycles, but also as indicators of pollution and mineral content on rocks. Lichens store numerous minerals in their thalli, their presence and concentration is indicative of the composition of the rock that they are growing on.