lichen

noun

li·​chen ˈlī-kən 

 British also  ˈli-chən

1

: any of numerous complex plantlike organisms made up of an alga or a cyanobacterium and a fungus growing in symbiotic association on a solid surface (such as on a rock or the bark of trees)

Note: The main body of the lichen, known as the thallus, is formed by fungal filaments which surround the photosynthetic algal or cyanobacterial cells. The lichen is usually described as having a leaflike (foliose), crusty (crustose), or branching shrub-like (fruticose) form. Lichens often play an important part in the weathering of rocks and include some that are sources of natural dyes.

2

: any of several skin diseases characterized by the eruptions of flat papules

lichened

ˈlī-kənd 

 British also  ˈli-chənd

adjective

lichenous

ˈlī-kə-nəs 

 British also  ˈli-chə-

adjective

Illustration of lichen

• lichen 1

Examples of lichen in a Sentence

Recent Examples on the Web

The often thinning plants allow the lichens more exposure to light and water plus nutrients from decomposing plant portions. —Tom MacCubbin, Orlando Sentinel, 23 Nov. 2024

Scientists have long argued if the Ediacara fauna were true animals and not some sort of large-bodied amoeba, lichens (!), or a completely extinct branch of life-forms. —David Bressan, Forbes, 18 Oct. 2024

Zayn Malik Postpones Shows, Cowell And Cole React Why Fungi Matter Fungi, including mushrooms, mold, yeast, mildew, and lichen, are critical to maintaining natural habitats. —Daniela De Lorenzo, Forbes, 20 Oct. 2024

Fortunato Gatto comes across a gnarled old birch tree adorned with pale ‘old man’s beard’ lichens. —Cecilia Rodriguez, Forbes, 9 Oct. 2024

Word History

Etymology

Latin, from Greek leichēn, lichēn, from leichein to lick

First Known Use

circa 1657, in the meaning defined at sense 2

Kids Definition

lichen

noun

li·​chen ˈlī-kən 

: any of numerous plantlike living things made up of an alga and a fungus growing together on a solid surface (as a rock or a tree)

Medical Definition

lichen

noun

li·​chen ˈlī-kən 

1

: any of several skin diseases characterized by the eruption of flat papules

especially : lichen planus

2

: any of numerous complex plantlike organisms made up of an alga and a fungus growing in symbiotic association on a solid surface (as a rock)