Mistletoe fact and fiction

By Irene Shonle
Director of Colorado State University Cooperative Extension in Gilpin County

My husband and I cut down our holiday tree the other day.  A few branches had mistletoe on them, so I held them over my head for a smooch.   This was somewhat in jest, because the dwarf mistletoe that we have around here hardly resembles the broad-leafed mistletoes of legend.

Two kinds of mistletoes are native to the United States: American mistletoe (the broad-leafed one associated with our kissing customs), and the dwarf mistletoe.  American mistletoe is found mainly in the eastern states, plus California and Texas, and mostly lives on hardwood trees.  Dwarf mistletoe is found mostly in the western United States and Mexico, and generally lives on pine trees.  Arceuthobium are known as dwarf mistletoes because of their lack of leaves and reduced visible growth habit.  They are of much less importance in the mistletoe legends, partially because they are relatively inconspicuous, and also because they are not much present on the European continent.

All the mistletoes grow as parasites on the branches of trees and shrubs.  In fact, the American mistletoe’s scientific name, Phoradendron, means "thief of the tree.”  Once the sticky seeds land on a twig, it produces root-like structures called "sinkers" that form each year.  Sinkers become embedded deep in the wood as twigs grow.  These sinkers provide the parasite with water and nutrients obtained from the host tree.   Eventually, the tree will die, but this takes a long time.  The broad-leaved American mistletoe is hemiparasitical, since it has green leaves and produces food for itself.  But our brownish dwarf mistletoe is fully parasitical, having no leaves of its own.  Most dwarf mistletoes are specific to a particular type of tree (i.e., lodgepole pines) and do not infect other tree species.

You may be thinking:  parasites don’t sound very romantic!  How did the kissing custom ever come about?  It’s actually not very clear.  However, from the earliest times the broad-leaved mistletoe has been one of the most magical, mysterious, and sacred plants of European folklore.  It was considered to bestow life and fertility, a protector against poison and an aphrodisiac.  Kissing under the mistletoe is variously thought to be associated with the Greek festival of Saturnalia, primitive marriage rites, or Norse mythology.  My personal favorite association is with peace; in Scandinavia, mistletoe was considered a plant under which enemies could declare a truce or warring spouses kiss and make-up.  No one knows for sure. 

Another part of mistletoe’s mystique may be because it stays green in the winter (again, remember that these legends refer to the European mistletoe), giving it a place along with holly, laurel, boxwood bushes and, of course, evergreen trees.  Displaying these evergreens during the darkest time of the year and is symbolic of the eventual rebirth of vegetation that will occur in spring.  Some people believed that the mistletoe in winter actually contained the life of the oak after it had lost its leaves the preceding autumn.

 Birds and Mistletoe

The plant’s common name — mistletoe — is derived from early observations that mistletoe would often appear in places where birds had left their droppings.  "Mistel" is the Anglo-Saxon word for "dung," and "tan" is the word for "twig."  Thus, mistletoe means "dung-on-a-twig."  Yet even though bird droppings cannot spontaneously generate mistletoe plants, birds are an important part of mistletoe life history — and vice versa.  Studies show that a high abundance of dwarf mistletoe in a forest means that more kinds and numbers of birds inhabit that forest.  Dwarf mistletoe flowers, shoots and fruits are food for insects, birds, and mammals.  The witches' brooms produced in severely infected trees may be used for hiding, thermal cover, and nesting sites by birds and other animals.

In other words, mistletoe is not all bad (unless you are the tree it kills).  In natural ecosystems, dwarf mistletoes have value as biological species and act as disturbance agents, influencing both the structure and function of forest communities.  When not in conflict with management objectives, mistletoes should be viewed as a natural component of healthy forest ecosystems.  So, the question becomes “how much is too much?”  That, unfortunately, is not a question that can be easily answered.  If every tree on your property is infected, the forest is not healthy, and will be more susceptible to pine beetles.  But a few trees here and there are not a problem, and may be a good thing.

Have a great holiday season, and if you want to see what mistletoe looks like, come check out displays in the Gilpin Community Center and the Exhibit Barn!  The Gilpin County Cooperative Extension office is located at the Exhibit Barn, 230 Norton Drive, Golden CO 80403 (right next to the Gilpin Community Center). Website: www.coopext.colostate.edu/gilpin, phone: 303-582-9106, email: irene.shonle@colostate.edu

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