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Definition: lichen from The Penguin Dictionary of Science

One of a group of specialized organisms comprising a mutualistic ➤symbiosis between a ➤fungus and an ➤alga or ➤cyanobacterium. Lichens are highly successful organisms. They have colonized environments that are hostile to other forms of life, such as deserts and high mountain-tops. They are frequently found growing on old stone walls and gravestones, but are highly sensitive to pollution, the presence of certain lichens being used as ➤indicator species for sulfur dioxide levels in the atmosphere.

lichen

From The Columbia Encyclopedia
(lī'kӘn), usually slow-growing organism of simple structure, composed of fungi (see Fungi ) and photosynthetic green algae or cyanobacteria living together in a symbiotic relationship and resulting in a structure that resembles neither constituent. There are about 25,000 species, most comprised of a sac fungus (Ascomycete) and a green alga of the genus Trebouxia or Trentepohlia or a cyanobacterium of the genus Nostoc; some lichens include multiple species of fungi, and more recently scientists discovered that basidiomycete yeasts are present in many lichens in addition. Lichens commonly grow on rocks, trees, fence posts, and similar objects. The body (thallus) of the lichen is made up of the filaments, or hyphae, of the fungus. Its typical greenish gray color is due to the combination of the chlorophyll from the photosynthetic organism with the colorless fungi, although sometimes the thallus may be red, orange, or brown. Lichens require no food source other than light, air, and…
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Full text Article lichen

From The Columbia Encyclopedia
(lī'kӘn), usually slow-growing organism of simple structure, composed of fungi (see Fungi ) and photosynthetic green algae or cyanobacteria living together in a symbiotic relationship and resulting in a structure that resembles neither constituent. There are about 25,000 species, most comprised of a…
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Full text Article lichen

From Dictionary of Microbiology & Molecular Biology
A ‘composite organism’ consisting of a fungus (the mycobiont) and an alga or cyanobacterium (the photobiont—cf. PHYCOBIONT ) in symbiotic association; a lichen thallus is morphologically and physiologically quite unlike that of either symbiont growing separately. Lichens are widely distributed, …
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Full text Article lichen

From Penguin Dictionary of Biology
A symbiotic association between a fungus (mycobiont) and a green alga (phycobiont), a cyanobacterium, or both, which develops into a unique morphological form quite distinct from either partner. Lichens are a biological, and not systematic, group. They are unique in that in many cases, although not…
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Full text Article lichens

From The Oxford Companion to Food
occasionally provide human and animal food. Some of these are popularly called ‘moss’, but lichens are different from mosses and only the former are edible. Lichens are biological curiosities. What appears to be a single plant is two, a fungus and a green or blue green alga. The two plants…
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Full text Article lichen

From Britannica Concise Encyclopedia
Any of about 15,000 species of small, colourful, scaly plants that consist of a symbiotic association of algae (usually green) and fungi ( see fungus ). These extremely hardy, slow growers often are pioneer species in sparse environments such as mountaintops and the far North. Fungal cells, anchored…
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Full text Article Lichen

From Black's Medical Dictionary, 43rd Edition
Lichen, or lichenification, is a term used to describe a thickening of chronically inflamed skin, giving rise to a tree-bark-like appearance. (neurodermatitis) is a form of eczema (see DERMATITIS ) perpetuated by constant rubbing of the affected skin. Typically, well-defined plaques occur on one or…
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Full text Article Lichen Planus

From Human Diseases and Conditions
Dr. P. Marazzi/Science Source. Lesions caused by...
Lichen planus (LY-kin PLAN-us) is a condition of the skin and mucous membranes 2215 that can cause shiny, reddish-purple bumps that may be itchy and painful, particularly near the genitals. The bumps may blister and cause patches of rough, scaly skin . Lichen planus is an inflammatory 2216 condition…
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Full text Article lichen planus

From Library of Health and Living: The Encyclopedia of Autoimmune Diseases
An inflammatory disease that affects the skin, mouth, and genitalia. It is characterized by recurring swollen blister-like eruptions on the skin or in the mucosa linings. Skin lesions are intensely itchy, generally reddish-purple in color, slightly raised, and scaly. Oral (mouth) lichen planus (OLP) …
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Full text Article Lichen Planus

From Gale Encyclopedia of Medicine
Lichen planus is a chronic condition that affects the skin. It produces rows of small, shiny, flat-topped, itchy, pink or purple bumps or rashes (spots) on the wrists, forearms, or lower legs, especially in middle-aged patients. It sometimes also affects the mucous membranes, such as those within…
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Full text Article FRUTICOSE LICHENS

From The Arctic Guide: Wildlife of the Far North Full text Article FLORA
FRUTICOSE LICHENS
Fruticose lichens are those whose thallus has no clearly differentiated upper and lower surfaces. They often resemble miniature shrubs, or hang down from branches in hair-like clumps. GENUS CETRARIA Iceland Lichen Cetraria islandica ALSO: Isländisches Moos, Mousse d'Islande, Islandslav, Цетрария…
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