As well as being used by herbalists, who use the parts to treat respiratory and circulatory problems, among other maladies, mistletoe has always had myths and traditions attached to it. It has been known as a symbol of fertility, an aphrodisiac, and currently a reason to kiss someone around Christmas time.
Mistletoe is a hemiparasite, or partial parasite. Like other parasitic plants, it grows on the trunk or branches of a tree and gets its nutrients by sending out roots that penetrate into the tree. Unlike other parasitic plants, mistletoe is also able to grow on its own and produce its food by photosynthesis. Although it is capable of surviving as a parasitic plant or on its own, it is more often found growing at least partially parasitically.
There are two main forms. Phoradendron flavescens, the mistletoe most often used as a Christmas decoration, grows as a parasitic plant on trees down the East Coast of the United States. Viscum album, the other kind, comes from Europe. Some ancient peoples, including the Greeks, thought it had mystical powers, leading much folklore to be associated with it. This form of mistletoe is green with sticky white poisonous berries and small yellow flowers. There are other related plants also known by the same name.
When mistletoe grows as a parasitic plant, it can end up damaging or even killing the host tree. The seeds are spread by birds eating the berries which are then spread via the birds droppings. When growing in trees, it also serves as a convenient support for birds' nests. In Australia alone, over 240 species of birds have been known to nest in this plant.
In Norse mythology, the god Baldur was slain by a weapon made of mistletoe. Druids gathered it at both the winter and summer solstice, seeing it as the soul of the oak tree it lived on as well as a symbol of fertility. Among the Celts and the Druids, it was thought to be an antidote to poison, even though the berries can cause a rash.
During the Middle Ages, mistletoe branches were hung from the ceiling or over doors to protect the house and the inhabitants from evil spirits. In parts of Britain, farmers used to give their Christmas bunch of mistletoe to the first cow to give birth during the New Year, supposedly giving luck to the whole herd. Some people believed that the plant could extinguish fire or that it appeared on oak trees during a flash of lightning.
The tradition of kissing under mistletoe may have begun with the Greek festival of Saturnalia, and was possibly used in some marriage rites, probably because it was thought to increase fertility. Some Britons today still burn their Christmas mistletoe to ensure that everyone who kissed under it have a chance at marriage. In Scandinavia, it used to be considered a "plant of peace." Enemies, or arguing couples for that matter, declared a truce while under the plant.
The custom of people kissing when they find themselves meeting under mistletoe is still common in the United States and many parts of Europe. According to "proper" etiquette, when a man kisses a woman under it, he should pick one berry. When all berries are gone from the sprig, the chance of kissing under it is gone.