In winter, woods can seem a bit ‘naked’ and empty. Trees and shrubs have entered into a dormant state in order to survive the rigours of the winter months. Their buds await the signals that herald Spring. Many birds will have migrated to warmer climes, some animals will be hibernating. Many insects will be spending the winter as eggs or pupae, whilst herbaceous plants will over-winter as seeds, corms or bulbs.  But on the bark of many trees and on the surfaces of fences and walls, there will be lichens – they are there in summer, winter, spring and autumn.  Lichens are rather unusual in that they are an amalgam of two (or occasionally three) organisms : a fungus and algae. They are symbiotic systems, where two partners work together for mutual benefit (occasionally there are more than two partners). The fungus makes up the bulk of the lichen’s structure (known as the thallus), but the algae (green algae or cyanobacteria) are essential as they can photosynthesise and provide the organism with carbohydrates.  The nature of the biochemistry and physiology of the lichen symbiosis is largely due to the pioneering work of Dr David Smith at the University of Oxford in the 1960's and 70's. Read more...