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

Chickadees and hummingbirds often use spongy moss and lichen as nesting materials. —Madeline Buiano, Martha Stewart, 10 Mar. 2026

Little white mushrooms and sprigs of grayish-green lichen dotted the ground. —Elizabeth Flock, New Yorker, 23 Feb. 2026

Mosses, ferns, lichens, and liverworts love it. —Condé Nast, Condé Nast Traveler, 21 Jan. 2026

To study how methyl mercury gets deposited, the researchers take samples of lichens, dissolving them in nitric acid to extract mercury and other metals. —Daniella Garcia Almeida, Mercury News, 13 Jan. 2026

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)