It can be pretty bleak at this time of year, waiting for the season to change and the buds to burst but look closely and there are still dazzling sights to be seen. This lichen caught my eye recently, clinging to a hawthorn. In fact, you will see this lichen on almost any hawthorn and many other trees and shrubs too. It is called Golden Shield, Xanthoria parietina, so named due to the golden, shield-like protrusions you can see in the photo.
Lichens are an incredible symbiosis between two separate organisms; a fungus and an algae or cyanobacteria. The two organisms form a mutually beneficial association with the lichen fungus creating a stable structure and the algae or cyanobacteria producing simple sugars through photosynthesis with which to feed the fungus.
No one really knows who benefits the most from this relationship. Is the fungus farming the algae for its own benefit, or does the algae gain more by being able to colonise a far greater area with the help of the fungus it clings too? It is a fascinating question with which lichenologists are still grappling.
Equally as interesting, especially to ecologists and conservationists, is the fact that lichens are excellent environmental indicators; they tell of current conditions and also how an environment may have changed, or not, over time.
In areas affected by atmospheric pollution such as acid rain, the communities of lichens surviving are likely to be severely impoverished. Species that may have been typical in the past are no longer present because lichens are sensitive to atmospheric composition. This is one reason why the Golden Shield may be found in hedgerows all around the UK; it thrives in nitrogen-rich environments like heavily-fertilised farmland.
Similarly, lichens are excellent indicators of ecological continuity. The presence of certain or groups of lichen can be used to help grade the conservation status of woodlands; a woodland that has been clear-felled at any point in its history is likely to have lost the original lichen flora that inhabited it. On the other hand, the lichens in an ancient woodland receiving minimal human intervention may be vanishingly unique.
Whether common or not, lichens are there to be enjoyed if we just take the time to look. Their often bright colours and small forms make them jewels of nature but their fascinating biology make them even more amazing.
More information about lichens can be found on the website of the British Lichen Society.