Mistletoe – a Plant Parasite
Facts About the Object of a Familiar Christmas Tradition
Mistletoe is associated with Christmas and kissing, but the natural history of this familiar group of parasitic plants is as interesting as the tradition and folklore.
Most Christians know mistletoe as the green bundle or sprig of leaves and white berries that we hang in the house at Christmas. For hundreds of years, it’s been a traditional stopping place for couples to kiss—a zone to linger in or scrupulously avoid, depending on the company.
Mistletoe is not just one plant. There are thousands of different species, divided up into the true mistletoes—American and European species, Phoradendron spp. and Viscum spp.—and dwarf mistletoe, Arceuthobium spp. All are parasitic plants, or more correctly, hemiparasites, of trees: they take water and nutrients from the plant they grow on, but also produce some chlorophyll and draw energy from the sun. Having no true roots, they produce structures called sinkers and haustoria, which penetrate host tissues.
Mistletoe in Folklore, Tradition, and Medicine
There’s more to mistletoe than Christmas kissing—the plant has a long and interesting history in human tradition and lore that continues today:
- Celtic druids believed that mistletoe contained the spirit of the tree in which it grew: this was the only part of the tree that stayed green all winter.
- In herbal lore, mistletoe is associated with communication, self confidence, romance, and an end to violence.
- Mistletoe has been used in exorcism and thanksgiving.
- In medicine, European mistletoe has been used as an antidote to poison, and to treat seizures and headaches. It’s currently being investigated as an anticancer treatment. Mistletoe can be quite poisonous however, so it’s unwise to experiment with homemade preparations!
True Mistletoe
References to true mistletoes are confusing: many people refer to American mistletoe as false mistletoe; however, botanically, Phoradendron spp. are true mistletoes, and are distinguished from dwarf mistletoes, which look quite different:
- True mistletoes can infest a variety of tree species: maple, apple, oak, thorn, poplar and others (although Phoradendron spp. and Viscum spp. have different host preferences).
- Mistletoes have male and female plants. Females produce white to red berries with sticky pulp and a single seed.
- Phoradendron spp. seeds and Viscum spp. seeds are distributed by birds in any of three ways. The seeds are eaten by birds and later passed in droppings, they are swallowed and then regurgitated, or they get stuck to the birds’ beaks and are rubbed into crevices on trees when the birds clean their beaks on the bark.
- Seeds mature over winter and germinate in the spring. The plant grows into the host initially and there may be no outward sign of growth for several years.
- A mistletoe infestation can be fatal to the host plant, but the decline takes many years. If the host dies, the mistletoe dies also.
- Viscum album is native to Europe, but it has been introduced to the United States.
- Mistletoe growing in the wild provides important food and nesting sites for birds.
Dwarf mistletoe
Like true mistletoe, Arceuthobium spp. live on trees, but they infest conifers, occurring farther north and causing more serious host disease:
- Dwarf mistletoe causes witch’s broom in trees—dense bushy abnormal growths.
- Arceuthobium spp. tend to be host specific, i.e. each species only parasitizes one species of tree.
- Dwarf mistletoe berries build up internal pressure until they burst, shooting the sticky seed many feet into the branches and needles of new hosts.
- Arceuthobium spp. don’t have leaves.
Dwarf mistletoes are not the species traditionally gathered at Christmas, and people have not been observed kissing underneath them.
Sources:
“True Mistletoes” and “Dwarf Mistletoes.” Young, Deborah, and Mary W. Olsen. CALS publications and videos. College of Agriculture and Life Sciences, the University of Arizona.
Natural Magick. Dubats, Sally. New York: Kensington, 1999.
