February 5: Lichen

The French Revolutionary Calendar celebrated Lichen on 5 February. 10 things you might not know about lichen.

1. Lichens have been around for a very long time: there are fossil records of lichens dating back at least 400 million years, possibly as far back as 600 million years, making them one of the earliest life forms to exist on land.
2. Yet, it wasn't until 1867 that scientists began to work out what lichens actually are. They are hard to classify because they are a symbiosis between two or even more organisms which all come from different kingdoms. There will be a fungus, algae and/or bacteria living together. Swiss botanist Simon Schwendener was the first to propose the theory that this was the case.
3. The word lichen derives from the Greek verb "to lick".
4. There are approximately 20,000 different species of lichen. They can survive in some of the most extreme environments on Earth - there are 200 species that can be found in Antarctica, but they are also found in rain forests, mostly living on trees. A single site in Costa Rica yielded about 300 species of lichen on leaves. Many live on bare rocks and stones. They can even survive in space for at least 15 days without suffering damage.
5. Lichens are food for some species of caterpillar, and they are also a significant part of the diet of reindeer. Reindeer can forage for lichens under the Snow.
6. Can humans eat it? Yes, although there are some species which are toxic - these are usually Yellow. In Japan and Korea they eat a type of lichen called Iwatake or Seogi. In parts of northern Europe, people once made soups, breads or Porridge from it. In some places it served as an emergency food in times of hardship. Peoples of North America and Siberia eat the partially digested lichen from the stomachs of reindeer they have killed.
7. Science has made use of lichen. Litmus, which is used to determine how acidic or alkaline something is, comes from a type of lichen commonly called 'orchella weed'. Also, because lichen grows very slowly and lives a very long time it can be used to date things, such as how long a rock surface has been exposed. The word for this is Lichenometry. Although lichens are tough, they can still be extremely sensitive to changes in their environment, so scientists can observe lichens to detect pollution and contamination.
8. Some lichens are natural antibiotics and have been used in herbal medicines.
9. Another significant use humans have put lichens to is to make dyes. 2,000 years ago, people were making Red and Purple dyes from lichens. In Scotland, the traditional Harris Tweed colours were once made from lichen. Another use to which humans sometimes put lichen is to make miniature trees and shrubs for model railways.
10. Lichen has even found its way into literature. In Ruth 3:8, the original Hebrew version uses the word "vayilafeth", which is interpreted as Ruth entwining herself around Boaz like lichen. More recently, John Wyndham's novel Trouble with Lichen is about an anti-aging chemical extracted from lichen.

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