By Charlotte Owen
It’s an everyday sight that can often go unnoticed but the more you look, the more of it you see – lichen growing on gravestones, bristling along branches, clinging to fence posts, encrusting rocks and daubed across rooftops. Look a little closer and you’ll notice that alongside the different shades of yellow, grey and green there are different structures too – some look like tiny branches of coral, others more like miniature tumbleweed, flattened leaves, tiny cups or a fine powder that seems completely ingrained in the bark of a twig.
These otherworldly organisms may seem plant-like but are actually a fusion of two very different life-forms. The first is a fungus, which forms the main body of the lichen, and the second partner is usually a type of green algae – the simplest form of plant life. Together they exist in a mutually beneficial relationship, with the fungus sheltering the algae from the elements and providing them with mineral nutrients, while the algae are busily photosynthesising to convert sunlight into energy, fuelling the lichen’s growth. Different combinations of fungi and algae produce different types of lichen, and there are more than 1,800 lichen species in Britain alone.
Thanks to this unique symbiosis, lichens have been able to colonise almost every nook and cranny on earth and can even thrive in the most extreme conditions, including the Arctic tundra – where lichen provides a vital source of food for reindeer. Growth rates are often very slow and sometimes as little as 1mm per year, with the most ancient lichen colonies estimated to be an incredible 9,000 years old. Throughout human history they’ve been put to a wide variety of uses, from packing material for ancient Egyptian mummies to a source of coloured dye for clothes, and the litmus dye found in every chemistry classroom is derived from lichen too. Some species have antibiotic properties and many are sensitive to atmospheric pollution, making them valuable indicators of local air quality. An area rich in lichens is usually rich in a variety of other species too, so there’s a lot to be learned from a closer look at lichen.