lichen

American  

[lahy-kuhn] / ˈlaɪ kən /

noun

lichens plural

1. any complex organism of the group Lichenes, composed of a fungus in symbiotic union with an alga and having a greenish, gray, yellow, brown, or blackish thallus that grows in leaflike, crustlike, or branching forms on rocks, trees, etc.

2. Pathology. any of various eruptive skin diseases.

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verb (used with object)

1. to cover with or as if with lichens.

lichen British  

/ ˈlɪtʃən, ˈlaɪkən /

noun

1. an organism that is formed by the symbiotic association of a fungus and an alga or cyanobacterium and occurs as crusty patches or bushy growths on tree trunks, bare ground, etc. Lichens are now classified as a phylum of fungi ( Mycophycophyta )

2. pathol any of various eruptive disorders of the skin

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lichen Scientific  

/ lī′kən /

1. The mutualistic symbiotic association of a fungus with an alga or a cyanobacterium, or both. The fungal component of a lichen absorbs water and nutrients from the surroundings and provides a suitable environment for the alga or cyanobacterium. These live protected among the dense fungal hyphae and produce carbohydrates for the fungus by photosynthesis. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. The more familiar lichens grow slowly as crusty patches, but lichens are found in a variety of forms, such as the tall, plantlike reindeer moss. The association between the different organisms in a lichen is so close that lichens are routinely referred to as a single organism, and scientists classify lichens using the name of the fungal component.

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Other Word Forms

Derived Forms

• lichenization
  noun
• lichen-like
  adjective
• lichened
  adjective
• lichenlike
  adjective
• lichenoid
  adjective
• lichenous
  adjective
• unlichened
  adjective

Inflected Forms

Nouns

• lichens
  plural

Etymology

Origin of lichen

1595–1605; < Latin līchēn < Greek leichḗn

Explanation

Have you ever walked through the woods and seen a crusty-looking shelf growing out of a tree? That is actually a lichen, a complex organism comprised of a fungus and its partner algae, the two parts interweaving to form one. The word lichen appeared around 1600, and was drawn from the Greek leikhēn, meaning "what eats around itself." This is a good meaning for what the word represents, as lichen is comprised of fungus cells that literally surround the algae cells to form a mutualistic bond. Because of the crusty look of a lichen, the name has also been given to a number of skin diseases that present the same patchy look as the fungus-algae.

Example Sentences

See Examples For:

lichen lichens

The same research group previously identified what may be the oldest known lichen fossil, also discovered in Mato Grosso do Sul and younger than the bacteria and algae described in the current study.

From Science Daily ● May 12, 2026

On the salvaged tiles alone, you can find salt efflorescence, water stains, fretting, lichen, smears of soot, scratches and gashes.

From Los Angeles Times ● May 8, 2025

The orange powder was removed from the stones using blown air, which has helped preserve the rare lichen on the surface of the stones, Mr Merriman confirmed.

From BBC ● Jun. 19, 2024

The plot of land where it sits originally held a logging shack; the ramshackle original structure still sits on the property, festooned by the passage of time by moss and lichen.

From Seattle Times ● May 6, 2024

They turned down Eliot Street where the smell of deepset gardens and the bark of aroused dogs followed them past old brick walls covered with lichen and ivy.

From "The Great Santini" by Pat Conroy

It is one of the region's largest oaks and a vital ecosystem for rare lichens like the black-eyed Susan.

From BBC ● Mar. 19, 2025

“If I were to make a prediction, I would envisage a growing fraction of the Peninsula’s landscape becoming dominated by a mosaic ecosystem of mosses, lichens, liverworts and fungi,” Roland said.

From Salon ● Oct. 19, 2024

Algae, pollen and lichens do accumulate in shady areas.

From Seattle Times ● Apr. 30, 2024

Nestled within the photosynthetic, or light-eating, tissue of the boreal trees -- and within the bountiful cloud-like lichens and feathery mosses that carpet the ground between them -- are fungi.

From Science Daily ● Feb. 20, 2024

Only moss, grass, lichens, and a few hardy flowers take root in the thin upper layer that thaws briefly in summer.

From "Julie of the Wolves" by Jean Craighead George