L i c h e n

Published on September 11th 2019
Lichen on a tree branch
If you’ve ever wandered in the garden, or hiked in the mountains, or simply brushed past a street tree, you would’ve noticed grey, green, yellow or orangey lichens growing on the branches of trees, rocks, fences, and even paving slabs.
Lichens are fascinating organisms and cover about 7% of the Earth’s surface. They can make themselves at home on just about any substrate and can survive severe conditions, some able to withstand great temperature extremes.
Lichens are not parasitic or harmful to plants and give the garden quite a mature look.
A close up of a tree branch

What is lichen?

Lichens are not plants, they are not even one single organism, but actually a union between fungi and an alga or cyanobacteria. This partnership is called symbiosis.

Symbiosis | Two or more organisms living in close association, usually to the advantage of both.

The algae photosynthesizes (let’s call it the ‘breadwinner’) and the fungus produces the structure and absorbs vapour from the air. Together they live in places where the two individual parts alone couldn’t.
Most lichens have an encrusted growth pattern, but some form hanging growth or leafy mats.
There are approximately 13,500 species of lichen and come in many different shapes, sizes and textures.
Lichens play a key role in numerous environmental processes like biological weathering where rocks are broken down to release minerals. Lichens are also excellent indicators of pollution and are used to monitor the concentration of pollutants present in an environment (known as lichen biomonitoring). Humans have used some species of lichen as food and sources of medicine and dye.
Lichen on a tree branch

Spot any lichen in your garden? See how many different types of lichen you can find and post them to the Feed using the hashtag #LookLichen!

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