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

An exploration of the close and enduring connections between Inuit, caribou, lichens, and land use. —Elaina Patton, IndieWire, 15 Dec. 2025

Now, this number may seem very high but included in this number are lichens and mosses which are considered plants. —Chris McKeown, Cincinnati Enquirer, 13 Dec. 2025

Unlike algae, which are lined with cell walls, lichen contain fungi lined with chitin, the same material that makes up the exoskeletons of insects. —Taylor Mitchell Brown, Scientific American, 25 Nov. 2025

Although the property already boasted mature trees and patches of existing mosses, lichens, and ferns, the artist’s path to arcadia was hardly straightforward. —Mayer Rus, Architectural Digest, 13 Nov. 2025

Word History

Etymology

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

First Known Use

circa 1657, in the meaning defined at sense 2

Rhymes for lichen

• glycan
• liken
• peptidoglycan
• proteoglycan

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)