By Joan Allen

Mistletoe is a popular Christmas decoration, not because it’s really all that showy, but because of the tradition of kissing associated with it (and maybe a bit because it’s evergreen). The origins of this tradition are a little fuzzy but it seems to be something that has been done in English speaking parts of Europe and the United States. It was first documented in the 16th century. This is not to say that mistletoe wasn’t important prior to this. Ancient Druids and people in medieval times believed that the plant had mystical powers, probably due in large part to the fact that it grew on oak trees and kept its leaves through the winter.

Anyway, back to the kissing. One theory holds that the tradition has its roots in Norse mythology. The story goes that the goddess Frigg (or the god Odin) had a son named Baldr. She wanted to protect him from harm and commanded all the plants not to harm him. She overlooked the mistletoe and a mischievous god named Loki tricked a blind god into shooting Baldr with a mistletoe arrow or spear, killing him. Being gods, they were able to resurrect him. Frigg declared that thereafter the mistletoe plant would be a symbol of love and peace instead of harm.

Another story tells of how single women in the ancient Babylonian-Assyrian Empire stood under mistletoe and were expected to become bonded with the first man who approached her. The practice of kissing under the mistletoe began to be mentioned in literature on a regular basis during the 18th century. At that time, a berry was removed from the plant prior to each kiss and once they were gone, there could be no more kissing. Etiquette dictated that the man must kiss the woman only on her cheek. In ‘The Sketch Book of Geoffrey Crayon, Gent,” Washington Irving wrote in 1820: “The mistletoe is still hung up in farm-houses and kitchens at Christmas, and the young men have the privilege of kissing the girls under it, plucking each time a berry from the bush. When the berries are all plucked the privilege ceases.”

But what type of plant is mistletoe? It’s a parasitic plant that only grows on trees, deriving its water, mineral nutrients and a portion of its carbohydrates from the host. There a few different types of mistletoe. The two main types in the U.S. are the dwarf mistletoes and the leafy mistletoes. Dwarf mistletoes are a serious problem in pines and other conifers, primarily in the west. The plants are small and brown. All mistletoes are true and flowering plants and are seed-producing perennials. Unlike the dwarf mistletoes, the leafy types do have leaves that contain varying amounts of chlorophyll, enabling them to photosynthesize and meet much of their own carbohydrate needs. They derive all their water and mineral nutrients (that are usually taken up from the soil via the roots in plants) from the host tree through little structures in the wood called sinkers. Leaves aren’t produced until a year or more after the sinkers are established. Flowering is late in the season and the white berries of the American true mistletoe (Phoradendron serotinum) mature just in time for the holidays. The tradition and myths described above are derived from the very similar European true mistletoe. Seeds are sticky and may fall from the plant onto the same tree where a new infection can occur. They are also dispersed by birds in two ways. If birds eat the berries, the seed is passed out on the other end of the digestive tract. Berries that stick to birds can also be carried to new trees where birds might dislodge them during preening.

American true mistletoes are not considered an important threat to the health of the host tree in most cases. This is largely due to the fact that they are drawing minimally on the carbohydrates produced by the host and primarily taking some of its water and minerals. Evolutionarily speaking, not relying on the soil as the source of your water and nutrients can be advantageous. The mistletoes originated in the tropics and began to spread northward and southward about 18,000 years ago. In the tropics, soils are often low in nutrients and there would be a lot of competition for both nutrients and water from other plants. The true mistletoes are not winter hardy so are not found north of the mid Atlantic states in the eastern U.S. American true mistletoe occurs on many hardwood deciduous trees.