Updated: Jan 8, 2022
Mysterious mistletoe is prolific in South West France, where I live, and is strongly associated with Christmas. But why?
The history of Mistletoe and its association with humans goes back to Greek and Roman times when it was used as a cure for everything from problems with the spleen to epilepsy. This is odd because it is in fact poisonous. All parts of the plant are poisonous - not normally lethally so, but demanding of medical attention. It was the Celtic druids, however, who really brought it to prominence in around the 1st century AD. They thought it sacred because it bloomed in the middle of winter and so they regarded it as a symbol of vitality and it became associated with celebrations surrounding the winter solstice and the rebirth of the sun.
More legends and superstitions surrounding fertility, life and vitality attached themselves to mistletoe until perhaps the 18th century. Things really took off then and mistletoe became an important domestic Christmas decoration, complete with the traditions associated with kissing beneath it.
Mistletoe is an unusual plant in that it is hemiparasitic, i.e. partially parasitic; it sinks roots (haustoria to give them the correct name) into the cambium layers of the bark of the host, penetrating its vascular tissues (the phloem and xylem), extracting nutrients and water, and so depleting the tree of these resources. However, because it has green leaves mistletoe contains its own chlorophyll and so can also photosynthesise its own food.
Healthy trees are not usually damaged by mistletoe but if a tree is weak or has a heavy infestation then it can suffer badly. When it attacks commercial trees, such as in apple orchards, it tends to be removed because it will weaken cropping. Mistletoe has a preference for certain types of tree - including apples, as already mentioned, and also oak, which is the principal host tree in Aquitaine.
If you want to control mistletoe then the easiest thing to do is cut it off. This will not remove it however, because the roots are still there and it will regenerate. If you bind the scar with black plastic to exclude light this will stop it re-generating, but it doesn't look very attractive, so is a perhaps a remedy best left to commercial growers. Pruning away the affected branch will remove it, but you need to cut well below the actual mistletoe plant to remove all of the haustoria. This is probably a remedy best left to a professional if the infestation is severe. There are also chemical remedies.
How does the mistletoe get there in the first place? Nature, as ever designs with intelligence. Birds eat the sticky white berries and the seeds are either scraped off onto a branch when they wipe their beaks, or they excrete the seeds while sitting high up in a tree. The excreta lands on the branch beneath them and the seed sprouts roots. It is all part of nature's grand pattern which, for mistletoe today, culminates in a kiss under a bunch of its leaves and berries at Christmas.