An Introduction to Lichen

Lichenometry is a tool of numerical dating that uses the size of lichen colonies on a rock surface to determine the surface's age. Lichen are not a single organism but a stable symbiotic association between a fungus (the mycobiont which give the structure) and photosynthetic algae and/or cyanobacteria (the photobionts which produces its own food by photosynthesis and then leaks some of this organic material that is then absorbed by the fungus, which cannot make its own food). When the fungus and algae and/or cyanobacteria they can live in areas when neither could survive separately. Some lichens grow so slowly that they liver for over 10,000 years. Lichens cover around 7% of the earth's surface, with some 650 species recorded in the Outer Hebrides and over 1500 species across Scotland.

It is a common misconception that lichen is a form of moss. This is in fact incorrect as mosses are considered ancestors of the plants around us, such as trees and flowers and have plant-like structures (leaves, stems and roots). Lichen do not have these common plant-like structures and only contain chloroplasts in the algae on the top surface of the lichen.

Interested in identifying lichen?

Then have a look at the Lichen identification workshop video...

There is a plethora of resources online, including:

• https://www.outerhebridesfungi.co.uk/lichens.php
• https://britishlichensociety.org.uk/learning/what-is-a-lichen
• https://www.scotlandguides.org/lichens-in-scotland.html
• https://forestryandland.gov.scot/blog/inside-the-complex-world-of-lichen
• https://www.encyclopedie-environnement.org/en/life/lichens-pioneering-organisms/