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.

---

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

---

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.

---

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

However, animal-free D3 made from sources such as lichen is also available, an important consideration for people following vegan or plant-based diets.

From Science Daily ● Oct. 8, 2026

He pointed out warblers, lace lichen and tree limbs coated in an orange algae called trentepohlia.

From Los Angeles Times ● Nov. 28, 2024

“A rich garden of life has grown on the megaliths, an exceptional lichen garden has grown. So it’s potentially quite concerning.”

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

He stood by a mighty blaze that popped and crackled, telling him when to add more wood, where to place dried lichen, and how to keep the fire from growing too enormous to control.

From "The Ugly One" by Leanne Statland Ellis

Both are small, with cone-shaped shells measuring about 6 mm in length, and they live on limestone rocks where they feed on algae and lichens.

From Science Daily ● Sep. 24, 2026

Glow worms, slime moulds and rare lichens are among 1,109 species discovered in just one corner of Scotland's rainforest.

From BBC ● May 21, 2026

“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

The danger bathed the world in a halogen glow that caused everything—the sweep of the rock, the orange and yellow lichens, the texture of the clouds—to stand out in brilliant relief.

From "Into the Wild" by Jon Krakauer