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Guided by lichens

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The Pharmaceutical Journal Vol 264 No 7095p680
May 6, 2000 Onlooker

Guided by lichens

battle cartoonMost people are blissfully unaware of the lichens that enrich their environment, often dismissing them as evidence of damp and decay. It is true that most lichens are humble in stature and appearance, although there are a few that can achieve remarkable colour and structure. One of their uncanny features is the ability to colonise all manner of substrates, from bare soil, hard rock, man-made edifices, trees and shrubs to old mine spoil-heaps, lightning conductors and industrial rubbish.
It is not often appreciated that the vigorous growth of a lichen upon a tree or an ancient stone has long served to guide travellers and give them an indication of their position in a landscape. In the fateful year 1066, for example, the Saxon King Harold ordered his military chiefs to bring their armies and assemble at the har-apple or hoar-apple tree on Caldbec Hill. The hoar-apple which formed the landmark was a tree bearing a vigorous coat of leafy lichen, which made it easily distinguishable from others, even from a distance.
Anglo-Saxon charters frequently designated the limits of villages and estates in terms of lines joining hoar trees, and these continued to be marked on maps. In addition to hoar-apples there were hoar-maples, hoar-hazels, hoar-thorns and especially hoar-oaks. Indeed, oaks were and still are greatly favoured by lichens and mosses, which find their bark a good source of nutrients and water. Our own two species of Quercus robur and Q petraea between them have been found to be associated with some 300 different species of lichen. Until the Elizabethan era there was no clear distinction made between lichens and the mosses which are commonly intertwined with them. Some of the coloured patches on trees made by lichens were not even recognised as living plants, but were merely weathering.
The adjective hoar means "grey-haired with age: venerable". As an indication of colour, it implies grey or grey-white. It also occurs in the noun hoar-stone, which implies an ancient stone or one grey with lichen. Like hoar trees, hoar-stones were mentioned in ancient charters as markers of boundaries. Often they were prehistoric standing stones erected near the summit of a hill and bearing a copious growth of bushy lichens as well as crustose ones. Most of these growths are many centuries old, and some have been on the stone for millennia.
It is one of the problems of lichenologists to discover the history of such stones in terms of human activities, since they may sometimes be traced to their quarry site by the nature and distribution of the many lichens to be observed on their surfaces. It is therefore deeply deplorable that we are now seeing a surge of vandalism directed against ancient monuments, which are disfigured by fire or hammers for no logical reason whatever. Once the surface of a hoar-stone has been severely burned the lichens embedded in it will take literally ages to show recovery, if they ever do. And some of the chemicals spread in agriculture do immense harm to lichen populations, whether on trees or on stones. Unfortunately, most people are unaware of their very existence, let alone their historical role.

Citation: The Pharmaceutical Journal URI: 20001378

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