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What are lichens?

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What are lichens?

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• An astonishing partnership between two very different organisms • Colonies which may be 9,000 years old • Colourful dyes for clothes • Packing for ancient Egyptian mummies! • Pollution indicators • High mountain dwellers and Arctic survivors Lichens present a very intriguing problem for people whose job is to name different kinds of organisms. This is because a lichen is not a separate organism in the sense of being one type of individual. It is actually a close partnership between a fungus and an alga. (Algae are very simple plants). The two types of organisms in the partnership are so closely interwoven that they appear as a single individual. This individual looks entirely different to either of the partner organisms making up the structure. Lichens are distinctive and they form many different, recognizable types. Many of these have been given specific names of their own, despite the fact that each lichen is already a mixture of different species. There are more than 1,700 species

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Lichens are autotrophic organisms composed of a fungus (sac or club fungus) and a photosynthetic unicellular organism (e.g., a cyanobacterium or alga) in a symbiotic relationship; they are resistant to extremes of cold and drought and can grow in marginal areas such as Arctic tundra.

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Lichens are ‘dual organisms.’ Every lichen is a partnership between members of two different kingdoms which live together in a special, mutually beneficial relationship (a symbiosis). Each lichen is made up of a fungus (usually an ascomycete) and an alga (green or blue-green). There are almost 20,000 lichens, each involving a different fungus, but the same algal partner can be found in many different lichens, so many fewer algae are involved. The body of the lichen is built up by tough fungal hyphae, and the algae live inside that framework. The fungus protects the alga from the harsh world outside, and provides it with water and mineral nutrients. The alga makes its own food by photosynthesis, and leaks some of this food, which is then absorbed by the fungus (which cannot make its own food). This partnership is so tough and self-reliant that lichens can grow in places like bare rock in deserts, where nothing else can survive. When it is too dry, too hot, or too cold, lichens go into a

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Have you ever seen a lichen and knew that it was a lichen? Not many people know what lichens are, and who would? They seem as though they are from another planet! Lichens are bizarre organisms and no two are alike. Lichens are a complex life form that is a symbiotic partnership of two separate organisms, a fungus and an alga. The dominant partner is the fungus, which gives the lichen the majority of its characteristics, from its thallus shape to its fruiting bodies. The alga can be either a green alga or a blue-green alga, otherwise known as cyanobacteria. Many lichens will have both types of algae.

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Lichens are peculiar organisms in which algae and fungi live together. They are usually flat and crust-like, with no roots and often grow on roofs, rocks or tree branches. Some grow like a small branched tree, while others can be found hanging from tree branches. The main structure of lichen is the fungal part, but it also contains algae cells which contribute food through photosynthesis. Lichens grow very slowly, but can eventually cover very large areas. Some individual ones are extremely old, and some lichens growing in rocks in Antarctica are thought to be 10,000 years old – they are the oldest living organisms.

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