Sunday, 6 January 2013

It takes two

On much of the county’s older stonework you will find round, crust-like patterns of rich ochre and sulphurous yellow. These are lichens, formed slowly over many years on this most inhospitable of substrates. Elsewhere, on rocks or ancient trees you will find other, more delicate, lichens that hang in limp shaggy forms. As a schoolboy these forms fascinated me, all the more so for knowing that lichens were not a single species but the result of a partnership between a fungus and an alga.

Time has moved on, and so has our understanding. While it is no longer strictly correct to think of a lichen by the definition with which I was schooled, it remains a convenient one to use, even if the alga is sometimes replaced by a cyanobacterium. I sometimes think of lichen as a form of fungal lifestyle, rather than a distinct taxonomic entity, even though each lichen is named after the fungal partner it contains. Roughly one in five fungi are lichenised but a much smaller number of algal or cyanobacterial partners are involved. A consequence of this is that some algae occur in a wide range of very different lichens.

Lichens have a long history and you will even find reference to them in some of the Anglo Saxon charters used to define village boundaries. These definitions used local features as a means by which the boundary could be interpreted; an ancient hazel hanging thick with lichen, for example. A tree that was shaggy with lichen would be described as ‘har’ (hoar) and it is from this root that we get hoarfrost. Lichens feature throughout the following centuries as food, dye for fabrics and medicine. The use of lichen as a medicine stems, in part, from the Doctrine of Signatures: the belief that the Creator had marked some plants as suitable for treating illness and disease through resemblance in form to that which they treated. The various forms taken by lichen meant that some were readily taken for use in herbal preparations, the lichen often steeped in milk or wine for several days. While the use of lichens faded as medical knowledge increased, it is interesting to note that the simple ‘acids’ produced by many lichens have basic antiseptic properties and some of the compounds present in lichens have been found to act on cancer tumours.

For those who study lichens there is much still to learn but for those, like me, who simply admire them with a very basic understanding there is much to appreciate, be it their colour, structure or ability to cope with difficult conditions. To see lichens on our buildings lends a sense of great age and a certain degree of character.

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