Mistletoe is a plant parasitic on the branches of a tree or shrub. European Mistletoe is easily recognised by its smooth-edged oval leaves in pairs along the woody stem and waxy white berries in dense clusters of 2-6 together. The species grows on a wide range of host trees and can eventually prove fatal to them where infestation is heavy, though damage more commonly only results in growth reduction. Almost all mistletoes are hemiparasites, bearing evergreen leaves that carry out some photosynthesis on their own and relying on the host mainly for water and the mineral nutrients it carries.

Most mistletoe seeds are spread by birds, such as the mistle thrush, who eat the berries. The seeds are egested in their droppings and stick to twigs, or more commonly the bird grips the fruit in its bill, squeezes the sticky coated seed out to the side, and then wipes its bill clean on a suitable branch. The seeds are coated with a sticky material called viscin which hardens and attaches the seed firmly to its future host. As we know, nowadays mistletoe is commonly used as a Christmas decoration and, according to English custom, any two people who meet under a hanging of mistletoe are obliged to kiss. Another custom, less known perhaps, is that the mistletoe must not touch the ground between its cutting and its removal at twelfth night. A tradition of the past was that mistletoe should stay hung up throughout the year - often to preserve the house from lightning or fire - until it was replaced the following Christmas Eve. The tradition spread throughout the English-speaking world but was largely unknown in the rest of Europe. As the mistletoe bears fruit at the time of the Winter Solstice, the birth of the new year, it is thought that it may also have been used in solstitial rites in Druidic Britain.