Why are lichens used as indicators of air pollution?
A lichen is a symbiosis: a fungus provides shelter and water while an alga (or cyanobacterium) photosynthesises food.
A lichen is a symbiosis: a fungus provides shelter and water while an alga (or cyanobacterium) photosynthesises food. This partnership absorbs minerals and gases straight from the air and has no protective waxy cuticle, so pollutants like sulphur dioxide poison it quickly. Lichens therefore vanish from polluted cities but thrive in clean air — their presence or absence maps air quality.
Key point
Lichens (fungus + alga symbiosis) absorb air pollutants directly, so they die in polluted air.
Common mistake
thinking a lichen is a single organism rather than a partnership.
Memory tip
no lichens on trees = dirty air; healthy lichens = clean air.
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