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Lichens cover about 7-8% of the Earth surface. These tiny organisms provide great lessons about the environment and are a great opportunity to take learning outside.
Lichen is actually two (or even three) organisms - a fungus and an algae or/and cyanobacteria - which form a unique symbiotic relationship. Simply put, the algae photosynthesises producing sugar for its energy but has no ability to produce minerals and moisture needed to prevent it from drying. The fungus, on the other hand, is unable to produce its own sugar but produces minerals and the structure necessary to survive in difficult conditions. In doing so, the two can come together and live in places where the individual parts alone couldn't.
As Robin Wall Kimmerer, celebrated botanist of an Indigenous heritage, beautifully put it, "[Lichens] carry teachings in the ways that they live. They remind us of the enduring power that arises from mutualism, from the sharing of the gifts carried by each species. Balanced reciprocity has enabled them to flourish under the most stressful of conditions. Their success is measured not by consumption and growth, but by graceful longevity and simplicity, by persistence while the world changed around them. It is changing now."
Lessons from lichens go beyond their reciprocal relationship. Unlike plants, lichens have no roots and absorb their nutrients directly from the atmosphere. Lichen communities are changing now because of their high sensitivity to air pollution. Different lichen species respond differently to various toxins in the air and some are more pollution-tolerant than the others. You can read more about it in this great research resource by the Natural History Museum. Lichens are also slow to adapt, meaning that the current speed of global warming might be too quick for them to keep up. In other words, lichens are strong indicators of air quality and changing climate.
Next time you take your students outdoors, get them to look around for the types of lichen that grow in your surroundings. Because of lichens' hardiness and their ability to grow on almost any surface, it is easy to spot them even in the most urban areas. Watch this short film on lichens in urban environments where lichenologists from the Royal Botanic Garden Edinburgh show how to find lichens around the city.