Being the festive season with mistletoe decorations and mistletoe kisses, this strange plant seemed a suitable subject for a blog, so here are some facts, superstitions and folklore...
As a plant without obvious roots or sources of food, it was once thought entirely magical and credited with extraordinary powers - giving rise to its use in medicine and a rich history of folklore. In the Middle Ages it was thought to break the death-like trances of epileptics, dispel tumours, divine treasure, keep witches at bay, and protect the crop of the trees on which it grew. Its use in the treatment of epilpsy continued into the 17th century and, as recently as 1993, a sixty-six year old man told of how, as a boy, he was given mistletoe by a gypsy woman to treat his epileptic fits, and that he had had no seizures since. I have seen mistletoe most commonly on Limes and Apples, but also on Hawthorn, Poplar, Willow, Rowan and False Acacia. It will undoubtedly grow on many other species but Pliny refers to its rarity on Oak, making 'Oak Mistletoe' highly valued for its 'powers' - Oliver Rackham questions if it is ever found on ancient Oak.
Enough myth and folklore - now for something completely different - a few mistletoe facts:
Mistletoe is in the Order Santales which includes the valuable and scented Sandalwood tree. The Order contains many epiphytes, parasites and hemi-parasites - including the Sandalwood tree itself which, when young at least, taps into the roots of a variety of host trees. Foresters growing Sandalwood in plantations will often use Acacia to start them off. Mistletoe is termed a hemi-parasite because its green leaves manufacture sugars by photosynthesis and it draws only water and mineral nutrients from the host.
There are over seventy species of Mistletoe worldwide, the European Mistletoe being the only one native to Britain. It prefers a mild, humid climate and good numbers of suitable host trees and is particularly common in a wide circle of land around the Severn estuary, where the valleys are moist and there is a tradition of fruit growing.
Whilst host trees can often tolerate some uninvited mistletoe, it can also be harmful, certainly killing branches and even whole trees if the 'infection' is heavy enough. Trees 'pull' water up through millions of tiny vessels, the pulling force being exerted by the osmotic pressure within the leaves and transpiration (evaporation) of water through leaf pores. The force is considerable and the millions of threads of water are as taught as piano wire. They can snap - something that is called cavitation but that a plumber might call an air lock, or a surgeon an embolus - and cells relying on the water from those vessels will die. Mistletoe can increase the tendency to cavitation and sometimes the water supply can give out and the host is killed by desiccation.