- Key People:
- Sir William Jackson Hooker
- Related Topics:
- beard lichen
- ascolichen
- Lecanora tartarea
- phycobiont
- mycobiont
lichen
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What is a lichen?
A lichen is a plantlike organism arising from a symbiotic relationship between algae or cyanobacteria and fungi. These organisms occur worldwide, thriving on tree bark, exposed rock, and as part of biological soil crusts. Lichens have three main body types: crustose, foliose, and fruticose.
The algae or cyanobacteria produce carbohydrates for the fungi, while the fungi offer shade and absorb water. Lichens can reproduce vegetatively, where pieces break off to form new growth. They are pioneer species that break down rocks and contribute to soil formation. Lichens serve as food for animals like caribou and have been used by humans for medicine, dyes, and food.
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What does it mean for an organism to be 'symbiotic'?
When an organism is described as symbiotic, it means it's involved in a close and long-term interaction with another organism of a different species. This interaction, known as symbiosis, can be one of several types:
* Mutualism Both species involved benefit.
* Commensalism One species benefits, while the other is not affected.
* Parasitism One species benefits at the expense of the other.Lichens are a prime example of a symbiotic organism, representing a community of different organisms rather than a single species. They are a composite of green algae or cyanobacteria and fungi. The alga or cyanobacterium provides carbohydrates through photosynthesis, while the fungus offers structure and protection.
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Which two main organisms form a lichen?
A lichen is a symbiotic organism formed by the combination of two main organisms: a fungus and either algae or cyanobacteria. The fungus provides structure and protection, absorbing water and nutrients from the environment, while the algae or cyanobacteria conduct photosynthesis, producing carbohydrates that nourish both partners. This mutually beneficial relationship allows lichens to thrive in diverse environments, colonizing surfaces like tree bark and rocks.
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How do the fungus and the partner (like algae or bacteria) help each other in a lichen?
Lichens are organisms formed through a symbiotic relationship between fungi and algae or cyanobacteria. In this partnership, the alga or cyanobacterium, being photosynthetic, produces carbohydrates that the fungi can absorb and convert. The algae may also produce essential vitamins for the fungi.
Conversely, the fungi benefit the algae by absorbing water vapor from the air and providing shade, which is crucial because algae can be sensitive to strong light. This mutual exchange of benefits allows lichens to thrive in diverse environments, colonizing surfaces like tree bark and rocks.
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Where can lichens be found in nature?
Lichens, fascinating symbiotic partnerships between fungi and algae or cyanobacteria, thrive in diverse environments worldwide. They colonize various surfaces, prominently adorning tree bark, exposed rocks, and forming part of biological soil crusts.
These resilient organisms are especially noticeable in harsh regions where few plants survive, such as bleak, far northern and southern areas, and high up on mountains. Different forms of lichens favor specific habitats, with crustose types dominating deserts and Arctic regions, foliose lichens flourishing in areas with frequent rainfall, and fruticose forms thriving in humid, foggy zones like seacoasts and tropical mountains.
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Why are lichens important for ecosystems and humans?
Lichens, a symbiotic association of fungi and algae or cyanobacteria, play a vital role in ecosystems and offer various benefits to humans.
Ecological Importance:
* Lichens are early colonizers, meaning they can grow on bare rock surfaces and start to decompose and create a thin layer of organic matter that helps with soil formation.
* They are an integral part of ecosystems on land and are extremely tough, surviving under harsh conditions.
* Lichens are also known as biological indicators of air quality.Human Uses:
* Lichens have been used by humans as food, medicine, and dyes.
* They produce unique organic compounds with antibiotic and antiviral properties, which may be used in medicine.
* Lichens are also used in some fancy perfumes.
* They provide two-thirds of the food supply for caribou and reindeer in the far northern ranges.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
lichen, any of about 15,000 species of plantlike organisms that consist of a symbiotic association of algae (usually green) or cyanobacteria and fungi (mostly ascomycetes and basidiomycetes). Lichens are found worldwide and occur in a variety of environmental conditions. A diverse group of organisms, they can colonize a wide range of surfaces and are frequently found on tree bark, exposed rock, and as a part of biological soil crust. Lichens have been used by humans as food and as sources of medicine and dye. They also provide two-thirds of the food supply for the caribou and reindeer that roam the far northern ranges. See also list of lichens.
Lichens were once classified as single organisms—until the advent of microscopy, when the association of fungi with algae or cyanobacteria became evident. Although lichens had been assumed to consist of a single fungus species (usually an ascomycete) and a single photosynthetic partner, research suggests that many macrolichens also feature specific basidiomycete yeasts in the cortex of the organism as well as specific bacteria. They are now properly understood as a community of organisms rather than a simple algae-fungi association. There is still some discussion about how to classify lichens, though many taxonomists rely on genetic analyses in addition to traditional morphological data.
The composite body of a lichen is called a thallus (plural thalli); the body is anchored to its substrate by hairlike growths called rhizines. There are three main lichen body types: crustose, fruticose, and foliose. Lichens that form a crustlike covering that is thin and tightly bound to the substrate are called crustose. Squamulose lichens are small and leafy with loose attachments to the substrate and are usually considered to be a special type of crustose lichen. Foliose lichens are large and leafy, reaching diameters of several feet in some species, and are usually attached to the substrate by their large platelike thalli at the centre. These lichens have a distinct top and bottom side and can be leafy, flat, or bumpy and convoluted. Fruticose lichens can be hanging or upright and may be hairlike, cuplike, or shrubby in appearance.
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In addition to their morphological forms, lichen thalli are also classified by the ratio of phycobiont cells (i.e., cells of the photosynthetic partner) to mycobiont cells (i.e., cells of the fungus). The homoeomerous type of thallus consists of numerous algal cells distributed among a lesser number of fungal cells, while the heteromerous thallus has a predominance of fungal cells.
Evolutionarily, it is not certain when fungi and algae came together to form lichens for the first time, but it was certainly after the mature development of the separate components. As symbionts, the basis of their relationship is the mutual benefit that they provide each other. The photosynthetic algae or cyanobacteria form simple carbohydrates that, when excreted, are absorbed by fungi cells and transformed into a different carbohydrate. In at least one case, Peltigera polydactyla, the exchange occurs within two minutes. The phycobionts also produce vitamins that the fungi need. Fungi contribute to the symbiosis by absorbing water vapour from the air and by providing much-needed shade for the light-sensitive algae beneath.
Lichens are long-lived and grow relatively slowly, and there is still some question as to how they propagate. Most botanists agree that the most common means of reproduction is vegetative; that is, portions of an existing lichen break off and fall away to begin new growth nearby.