lichen

American  

[lahy-kuhn] / ˈlaɪ kən /

noun

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

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

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

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

Ms Nouvet, a rainforest advisor with PlantLife, a member of the Alliance for Wales' Rainforests, said the fallen tree's bark was once home to more than 60 types of lichen.

From BBC • May 18, 2025

Functional for the outdoors, jackets are cut from cotton gabardine, wool and cashmere for warmth, while the Burberry Check is reworked in earthy colorways like sand and lichen.

From Los Angeles Times • Sep. 3, 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

Some of the trees had moss and lichen growing on them.

From "Fablehaven" by Brandon Mull