# lichen

/ˈɫaɪkən/ (US) · /lˈaɪkən/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/lichen
Updated: 2026-05-27

## Definition

a small plant that grows on rocks, trees, or walls. It is actually a mix of two different living things working together.

For teachers: a composite organism that arises from the symbiotic relationship between a fungus and a photosynthetic partner, such as an alga or cyanobacterium.

## Examples

- The old stone wall was covered in green lichen.
- Because lichen is very sensitive to air quality, scientists often use it to measure pollution levels in a forest.
- The lichen's ability to survive in extreme environments, such as the polar regions or the surface of a rock, makes it a subject of interest for astrobiologists studying potential life on other planets.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.