‘Why don’t you write a post about lichen?’ the SF asked recently, inspired by the plentiful specimens adorning the walls of our barn. What I knew about lichen would go on the proverbial postage stamp – not that this usually prevents me from writing about something, but since people devote their lives to studying the things I might be at a certain disadvantage. However, the more I thought about it, the more I realised that lichen is a distinctive – if unobtrusive – feature of life in rural SW France.
What is lichen? Before I did some research, I had no idea that it is not a single organism but a structure composed of two organisms – a fungus and an alga. They cohabit in a symbiotic relationship. In most cases, each can exist without the other in nature but in a few cases the fungus has become entirely dependent on the alga for its survival. The fungus needs carbon as its food source, which the alga provides via photosynthesis.
A great diversity of lichens exists. Some occupy a wide range of habitats while others need very specific and limited conditions in order to survive. Of course, there is much more to it than this and I’m not going to try to delve into it much further. But I found the British Lichen Society’s website very helpful in expanding my minimal knowledge.
What’s so important about lichens? They are a very sensitive indicator of air pollution and a possible means of gauging climate change. In heavily industrialised areas with coal-burning industry and power stations, very few lichens were able to exist and only one species thrived. Equally, and probably more important these days, agriculture and exhaust fumes produce nitrogen oxides that are toxic to some lichen species.
So when I say that lichen is a distinctive feature down here, it’s because it shows we enjoy low levels of certain types of air pollution. In fact, it colonises just about anything that is left outside long enough: walls, trees, shrubs, some aluminium garden chairs we brought from England and even the rubber trim on our 16 year-old car.
More than anything, though, it is strikingly beautiful when it glows in the sunlight on an old stone wall. The colours range from the usual green, through yellow, orange red and even white. I understand that these colour changes occur because of substances breaking down within the composite organisms.
Whatever the chemical reason, I find they embellish the ancient stonework in a way that enhances its natural beauty. Unfortunately, I also read that the waste from lichen eats into the stone, but it might take 900 years or more to do it (there’s some controversy about how long they can live), since it is very slow growing and long lived. I’ll just continue to enjoy it, then.
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