You may not have noticed lichens and mosses. They seep into a landscape, growing on walls, trees, even gravestones, but these amazing organisms are actually extremely complex, and hugely beneficial to our environment. Nature’s Home columnist Nicola Chester tells us all about lichens.
Up close, lichens can look like tiny forests themselves, like this species Hypogimnia sp., pictured at RSPB Abernethy. Photo: Andy Hay (rspb-images.com)
What is a lichen?
Lichens are actually two organisms, an alga and a fungus (and sometimes cyanobacteria), living in a symbiotic sandwich. The fungus is the main body of the lichen, protecting the alga within. They are self-sufficient, not feeding off the surface on which they grow, but instead the alga creates food through photosynthesis. Photosynthesizing algae or bacteria provide carbohydrate food for both organisms, and the fungi provides a protective home.
A trip out with a hand lens will transport you to a complex, miniature world of forests and fairy cups. They are incredibly adaptable and versatile, with different species evolving to live on everything from patios to old gravestones, rocks, buildings and trees. Some like the acid bark of a birch or alder, while others favour the smooth, less acidic bark of a hazel. The community of lichens on a young oak will change as it ages, because the bark becomes more alkali with maturity.
They grow in some of the most extreme environments on Earth and have even survived space travel. Growth is slow and some lichens are thousands of years old. The UK’s 1,700-odd lichen species are mainly crustoaly (squamulose), leafy (foliose), or bearded (fruticose).
Mosses are simply plants while lichens are made up of two organisms. Photo: Colin Wilkinson (rspb-images.com)
What’s the difference between a moss and a lichen?
While lichens are made up of two organisms, mosses are simply plants. Mosses pre-date dinosaurs and perform a vital role in the forest ecosystem. Some are so exuberantly luxuriant that they can soak up rain. Sphagnum, for example, can store many times its own weight in water. By doing so, mosses help the atmosphere remain moist, as the water gradually evaporates. Because moss will grow on nearly anything that that doesn’t move it reduces erosion and the run-off of soil into rivers.
Lichens are good for wildlife, beneficial to use and they're a good indicator of a healthy environment. Photo: Andy Hay (rspb-images.com)
What’s so good about lichens?
The humble lichen is a miniature habitats for spiders and other insects, including tardigrades, and are grazed by slugs and snails. One of their most beautiful and clever uses is in the nests of long-tailed tits. These “lollipop” shaped birds build soft, warm, expandable nests out of scraps of moss, hair and spider web. The outside of the nest is camouflaged and “tiled” with up to 3,000 flakes of lichen, that stick like Velcro, effectively waterproofing it.
And lichens are good for us, too, bring used in pharmaceuticals, for sunscreens, wool dyes and perfumes. They are Dave Lamacraft, lichen expert from Plantlife, explains: “Lichen has such interesting biology, bringing so much potential for humans. Some offer UV protection and some have the potential to treat cancers. The old-man’s beard lichen contains usnic acid, which is considered more effective than penicillin against some bacteria. We’ve only just touched on the capacity of these organisms.”
Extracting water and nutrients from the air, lichens are also important indicators of a healthy environment. Crusty lichens are more pollution-resistant, whereas bearded ones are mostly found in cleaner locations. Lichens simply cannot survive without good air quality.
There are a vast array of species of lichen. This is Cladonia portentosa, seen at RSPB The Lodge. Photo: Jodie Randall
Species of lichens
Here are just a few species you can look for.
Tree lungwort (Lobaria pulmonaria) – This lichen is known as the lungs of the forest. The loosely attached, leafy lobes have a distinctive network of ridges and a the lichen has a history of medicinal use – believed to help with respiratory disorders. With its lung-shaped foliage, it is instantly recognisable but there are around 200 species of varying colour, shape and structure.
Octopus suckers (Collema fasciculare) – This jelly lichen looks like clusters of tiny, dark octopus suckers. It performs a useful role in the ecosystem, taking nitrogen out of the atmosphere and making it available as fertiliser to other organisms.
Blackberries in custard (Pyrenula hibernica) – This lichen doesn’t look quite as appetising as its name implies. Black fruits grow out of the smoother, yellowish lichen. It is globally very rare and prefers the bark of hazel trees.
Floury dog-lichen (Peltigera collina) – Grey lobes are surrounded by raised frilly margins, which contain powdery granules that are mini-packages of the alga and fungus. The underside is the supporting structure, which resembles dog’s teeth.
Bloody heart lichen (Mycoblastus sanguinarius) – This lichen is made up of small black lumps that grow on acid bark, such as young oak trees. If scratched, the lumps reveal a stark and surprising bright white and red interior.
Stinky stictas (for example Sticta sylvatica) – The sticta family of lichen smell of fish when wet. A gentle rub of this frilly lichen will release the distinct fishy odour, but if you do so be warned – the smell is particularly pungent and lingering.
Lob scrob (Lobaria scrobiculata) – Strangely colour-changing, this lichen is creamy yellowish when dry, but more blue-grey when wet. It has been discovered that this lichen contains a compound that can treat BSE or “mad cow disease”.
You can read more about lichens and their habitats in the January issue of Nature's Home magazine. If you're not yet a member, sign up to receive your free copy.
I think the link between lichens and air quality is more complex. Some species are growing better because of the presence of higher levels of atmospheric nitrates - a pollutant.
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