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Lichen is a hidden gem in our woodlands, often overlooked and underappreciated. 

Scotland is home to over 1,500 different species of lichen, which makes up around 87% of all lichen found in Britain. Lichens tend to thrive in our relatively clean air, cool summers, mild winters, and our higher levels of rainfall which occur throughout the year. This is especially true of western Scotland, which is home to a large number of rare species and other lichens that live in Scotland’s Rainforest, part of the globally rare temperate rainforest. 

These hearty organisms may look simple, yet they are more complex than we often realise. Lichen occurs when two or more organisms come together, creating a symbiotic relationship. A symbiotic relationship is when these organisms are so intertwined they often evolve together, like flowers and bees. 

In the lichen’s case, we have a connection between fungi and alga/blue-green alga. The fungus is the ‘body’ of the lichen, which protects the alga within it, with its intertwined sting-like fungal cells. The alga/blue-green alga provide food as sugars to the fungus through photosynthesis.   

With lichen, the importance of the relationship differs depending on whether you are the fungi or the algae. Though both organisms benefit from the relationship, the algae can survive on their own, while the fungi need the algae to survive.  

Lichens are rootless, and instead, take in water directly from the atmosphere, this makes them robust organisms that can grow in harsher environments than most, such as deserts, mountaintops, and frozen landscapes like tundra. In dry conditions they shut down their systems and dry to a crisp. Most lichens look fairly drab when they dry up, but brighten with a whole range of intense colours when wet. 

Because lichens take in water directly from the atmosphere they can be very sensitive to pollutants, causing them to be more susceptible to changes in our rainwater. 

We have seen many species of lichen in decline, some becoming locally extinct because of human-related toxins such as sulphur dioxide, ammonia from animal farming, atmospheric nitrogen oxides from exhaust fumes, and other pollutants like ozone.

However, this sensitivity to change makes lichens useful ‘indicator species’. An indicator species is one that is environmentally sensitive and can therefore help scientists predict changes in like air quality.

When it comes to air, lichens are used because their level of sensitivity can vary such that we can tell how polluted an area is by the type of lichen growing in it. In areas with lots of agriculture and vehicle traffic, you will see ‘crusty’ lichen. In areas with little air pollution, you’ll find more nitrogen-sensitive or ‘bushy’ and ‘leafy’ lichens that can only survive on clean air. 

Lichen identification can be a fun activity to do year-round, and Scotland is a perfect place to learn more about these delicate organisms that add personality and colour to our woodlands. Though you should be able to find lichen rather easily, we recommend these locations to go spotting for this underrated organism.

Old mans beard lichen on tree branchesUsnea or old man's beard lichen. 

Our favourite lichen forests: