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 huge piece was pitted like a Holland cheese and carried on its irregular surface some splotches of green and snuff-yellow where the lichens clung in spotted patterns. —Frank C. Hibben, Outdoor Life, 27 Feb. 2025

Moss and lichens gradually die when on the ground and do not have to be gathered. —Tom MacCubbin, Orlando Sentinel, 15 Feb. 2025

Those are lichens growing on the surface of the grapefruit bark. —Tom MacCubbin, Orlando Sentinel, 18 Jan. 2025

The scientists discussed pioneer species — like moss, mold and lichens — which could be introduced to Mars and set the stage for terraforming the planet. —Tom Brown, Space.com, 9 Jan. 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)