What is a lichen? This question has been the subject of much debate in the past. Many people know that lichens are composite organisms, comprising a fungus and a cyanobacterial or algal partner, but the situation may in fact be far more complex. A great number of other microbes have been identified living within the tissues, and there are some tantalising indications that these may also play a role in the functioning of lichens. David M. Wilkinson discusses the current understanding of lichen biology and explains why there is still much to learn about these intriguing organisms.
Lichens are perplexing organisms. Set aside any relevant knowledge that you may have, and consider them afresh – it really is not clear what you are looking at. Perhaps they are plant-like? After all, many lichens are obviously alive but they are surely not animals.