Mistletoe and Holiday Traditions - December 14, 2011
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

Mistletoes are perennial flowering plants that are parasitic on aboveground portions of woody plants. They have specialized roots with the ability to penetrate a host plant and absorb nutrients. North central Arizona has an seven species of true mistletoes and eight species of dwarf mistletoe. True (or leafy) mistletoe (Phoradendron spp.) has green leaves and white berries and is found on a variety of hardwood species, junipers, and cypress. Dwarf mistletoes (Arceuthobium spp.) are leafless and can be yellow, orange, brown, or green. Dwarf mistletoes only affect needle-leafed conifers and are rarely noticed by casual observers. There are several other mistletoe species found around the world.

True mistletoe plants are perennial and remain alive within their respective host until the tree host or the branch upon which it is established dies. True mistletoes photosynthesize to meet their carbon requirements (making sugars). They rely on the host plant to provide water and mineral nutrients carried by the water. While they are parasites in that they must have a living host, they do not necessarily cause a debilitating nutritional drain on the host. A few true mistletoe infections on an otherwise healthy plant cause minimal harm to the host. However, the portion of a branch beyond the point of a single infection may become stunted in growth and even die prematurely. Multiple infections can place significant stress on the host which can lead to premature death or weaken it to the point that it may be more susceptible to another disease or insect pest.

In situations such as orchards, where there may be economic impacts, infected branches can be removed. Care must be taken to remove all of the infection in the branch, as any living mistletoe tissues that remain in the host are capable of regenerating into whole plants. Some herbicides are available to treat mistletoe infections, but this is not a permanent solution because the mistletoe grows back.

Mistletoe is dioecious (having separate male and female plants) and is spread by seeds. The seeds become sticky when wet and can fall on neighboring branches or plants. The berries are also eaten by birds. As the birds fly from tree to tree, the ingested seeds pass through the gut. Birds then deposit their excrement with mistletoe seeds on the branches of trees where they perch. These mistletoe seeds may germinate and parasitize a new host plant. The origin of the word "mistletoe" appears to come from the Anglo-Saxon words "mistel" which means dung and "tan" for twig. Mistletoe literally means "dung-on-a-twig."

Pliny the Elder (23 to 79 BC) wrote detailed descriptions of the attitudes of people toward mistletoe. He recorded the widely held belief that whatever grew on the sacred oak was sent from heaven and, since mistletoe was only occasionally found on the oak, it was indeed cause for celebration when it was encountered. Pliny also recorded the belief that the mistletoe in winter contained the life of the oak after it had lost its leaves the preceding autumn. It was believed that the mistletoe plant was protected in some mystical sense from injury or harm. If it was cut from the oak, it retained some of these mystical powers, which could be channeled as healing powers. However, if it touched the ground after it was harvested, its healing powers would be lost.

There is an old rule that governs kissing under mistletoe that is rarely followed by today’s practitioners. The rule says: a man might steal a kiss under the hanging mistletoe branch, but when he does, one berry must be plucked from the plant and discarded. Once the berries are gone, the kissing charm of the mistletoe branch is spent. When I sold mistletoe as a kid, I had no idea that I was selling parasites that originated in bird dung which caused grown-ups to kiss each other while concurrently increasing fertility and repelling evil.

Being serious for a moment, I hope that you have a chance to slow the pace of your lives, joyfully celebrate any and all holidays, and find new ways to appreciate the short days and cool temperatures of winter.

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: December 8, 2011
Content Questions/Comments: jschalau@ag.arizona.edu
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