Mistletoe, primarily the European species Viscum album, is the festive decoration commonly hung during the winter holidays that is botanically a parasitic plant. With its waxy white berries and evergreen leaves, it maintains a deceptive appearance of health even as its host trees enter winter dormancy. Mistletoe is an epiphyte, meaning it grows upon another plant, but unlike non-parasitic air plants, it actively extracts resources from its host.
The Biology of a Parasite
Mistletoe is classified as an obligate hemiparasite; it must grow on a host plant to complete its life cycle, though it retains the ability to perform some photosynthesis. Seeds are often dispersed by birds, whose sticky droppings carry them to new branches. Upon germination on the host tree’s bark, the seed develops a specialized root-like structure called a haustorium.
The haustorium penetrates the host tree’s bark and tissue, forming a direct connection with the tree’s vascular system. It taps into the host’s xylem, the tissue responsible for transporting water and dissolved inorganic nutrients.
As a hemiparasite, mistletoe possesses chlorophyll and performs photosynthesis to produce its own sugars. However, it is entirely dependent on the host for water and mineral supply. Some studies indicate that certain species may also derive a percentage of their carbon (sugars) from the host, with estimates ranging from 24% to 62%.
The constant draw on the host tree’s resources can be detrimental, especially when multiple mistletoe clumps infest a single branch or tree. The presence of the parasite can reduce the host’s overall vigor, slow its growth, and even lead to the death of branches or the entire tree in cases of severe infestation. This makes the plant an agricultural pest in some regions, despite its romantic cultural associations.
From Pest to Symbol
Before its adoption as a Christmas decoration, Mistletoe held deep spiritual and mythological significance across ancient European cultures. The Celtic Druids, in particular, revered the plant, especially when it was found growing on the sacred oak tree, which was a relatively uncommon occurrence. They viewed it as a powerful symbol of vitality and fertility, since it remained green and produced fruit during the barren winter months.
Druidic rituals, documented by the Roman naturalist Pliny the Elder, involved priests harvesting Mistletoe using a golden sickle. This sacred collection was believed to offer protection from evil and was used in medicines. Its ability to seemingly grow without roots led to associations with spontaneous generation and life itself.
The plant also features prominently in Norse mythology, specifically in the tale of the god Baldur, the son of the goddess Frigg. Baldur was prophesied to die, so his mother extracted an oath from every element of nature not to harm him, but she neglected the seemingly insignificant Mistletoe, which did not grow on the ground. The mischievous god Loki then fashioned an arrow or spear from Mistletoe, which was used to kill Baldur. In one version of the myth, Frigg’s tears over her son’s death turned the red Mistletoe berries white, and she declared the plant a symbol of love and peace, promising a kiss to anyone who passed beneath it. This mythological association also contributed to an ancient Scandinavian custom where enemies who met under a Mistletoe-bearing tree were required to lay down their arms and observe a truce for the day.
The Tradition of the Kiss
The specific custom of kissing beneath a sprig of Mistletoe is a more recent development, primarily traceable to 18th-century England. While older folklore established its connection to peace and fertility, the romantic practice emerged within the lower classes before spreading to all societal levels.
A distinct ritual was often attached to the practice in its earlier form, which involved plucking a berry from the Mistletoe after each kiss. The custom dictated that the kissing privilege would cease once all the white berries had been removed from the sprig.
The custom’s popularity was further cemented in the United States by American author Washington Irving, who described the practice in his 1820 book, The Sketch Book of Geoffrey Crayon, Gent. His writings detailed the English Yuletide traditions he had observed, including the rule that a young woman caught under the Mistletoe could not refuse a kiss.