Over millions of years lichens have quietly colonised the planet from the Poles to the deserts. They can tolerate the harshest environments on Earth - and even outer space. Lichens are neither plant nor animal. The power of the electron microscope reveals that lichens are a combination of a fungus intertwined with a green alga, or cyanobacterium. This symbiotic relationship is so successful that lichens are able to colonise barren wastelands and survive extreme conditions long before any other life forms can emerge.