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NatureWatch in Matterdale

A One Sheet Introduction to Lichens


Lichens are stable communities in which a fungus (the mycobiont) interacts with an alga, or sometimes a cyanobacteria (blue green algae) or sometimes both. The fungus provides “shelter”, the alga/ cyanobacteria (the photobiont) makes sugars (food). Recently lichenologists have found yeasts playing a role too. They (lichens) are beautiful, fascinating and enigmatic. 

Lichenologists use some long and complicated words. But there is usually a simple(ish) equivalent. Most lichens have no English common name, so Latin names are the norm (sorry). 

Lichens cover about 8% of the earth’s land surface. Different lichens thrive in different environments, and grow best on different things. They can’t control the water or chemicals that land on them, and they can’t run away, so are vulnerable to pollution. They can live for a long time and tell us stories about landscape and the environment, about pollution and woodland history. 

How to identify lichens 

Most lichens- and their features- are small. A hand lens (x10 magnification) is very useful. After a while, most people who are interested start using a microscope to see the exceedingly small parts. 

We can divide lichens by their growth forms: 

· Leafy (foliose)- like “leaves”, with an upper and lower surface 

· Crusty (crustose)- hard to remove to from what they are growing on 

· Fruity ( fruticose)- sticking up or dangling down with no upper/ lower surface difference 

· Leprosy (leprose) – powdery 

· Squamulose - little lobes 

· Jelly- swell when wet 

How lichens reproduce is important in identification: 

Sexual reproduction (by the fungus) involves spores being produced in a fruiting body: an apothecia (often disc-like) or a perithecia (a flask shaped like a pimple). Many apothecia are like “jam tarts” (lecanorine) or a “wine gum” (lecideine). Some look like writing (lirellae). 

Asexual reproduction: this is basically bits falling/ being knocked off. Common ways involve soredia (a powder); isidia (little pegs); or just by bits falling off. 

Lichens everyone (in Cumbria) should know 

Rhizocarpon geographicum: the map lichen. Greeny-yellow crust found on acid rock. 

Xanthoria parietina: the sunburst lichen. Yellow/orange (or blue/green in shade) lobes. Likes nitrogen enrichment. Grows on trees, rocks, barns, road signs, coastal rocks, cars… 

Normandina pulchella: “elf ears”. Grows on mossy trees, usually less acid ones. 

Lobaria pulmonaria: “tree lungwort”. Huge leaves. Likes clean air and older, not-so acid barked trees. Much affected in Cumbria by the pollution of the last 250 years and hasn’t really recovered. 

Peltigera species: “Dog Lichens”. Big and leafy. Found on mosses, rocks, walls… 

More info from: 

Pete Martin, November 2022
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