Garden Tips: Mistletoe may be cute above door frame, but it’s a parasitic plant

My childhood holiday memories include the hanging of mistletoe above the door to our living room. These were sprigs of real mistletoe that we bought at the store, not the plastic ones available today.

Mistletoe is an odd plant to be associated with Christmas traditions, because it was originally a part of ancient mid-winter pagan practices that involved cutting mistletoe with a gold knife and making animal and human sacrifices. That is a very long way from giving sweet kisses beneath the mistletoe!

Surprisingly, it was probably the staid British Victorians who started the modern tradition of kissing under mistletoe, borrowing from the plant’s place in Viking mythology. As the myth goes, the summer god of the sun, known as Balder, was accidentally killed by his blind brother with an arrow made from mistletoe wood. His mother, the goddess of love and beauty, was grief stricken and begged nature to bring him back to life. When Balder was revived, his mother was so happy that she proclaimed that anyone who passed under mistletoe should receive a kiss as a symbol of love.

I wonder why the Christmas mistletoe tradition has waned in recent years? Perhaps it is because the entire plant, especially the berries, is considered poisonous. Ingestion of leaves or berries can cause digestive irritation, diarrhea, cardiovascular collapse and even death. Labels on packages of fresh mistletoe provide warnings against children and pets eating any parts of the plant. Because berries readily drop off mistletoe as it dries, remove the berries before hanging. Some sprigs are sold with plastic berries in place of the real ones.

Even though mistletoe has been around for a long time, most of us do not know much about it. It is a partially parasitic, or hemiparasitic, plant that lives off of other plants. It starts as a seed that germinates and develops rootlike structures that grow on its host’s surface. The young mistletoe plant then develops a penetration peg that goes through the surface of the host and into the tissues below. Next, the mistletoe produces sinkers that connect it with tissues below the surface and enable it to absorb nutrients and water from its host. Some types of mistletoe also develop leaves and are capable of photosynthesis. As mistletoe plants mature, they develop into shrublike twiggy growths.

Mistletoe is considered a plant disease, and its hosts are most often woody trees and shrubs. Unless severe, a mistletoe infection usually does not kill its host. Mistletoe typically weakens infected trees and shrubs, making them more susceptible to attack by other diseases or insect pests.

The type of mistletoe most associated with the holidays is commonly found infesting cultivated apples, lindens, poplars and hawthorns in Britain and Europe. Around the world, there are at least 1,500 species of mistletoe, with most growing in the warmer regions of the globe.

In Washington and Oregon, there are dwarf mistletoes that infect Douglas fir and other conifers. You might have seen mistletoe without knowing it. An infection leads to a “witches broom” that looks like a tight mass of twigs and needles growing within the tree.

Meanwhile, the tradition of hanging mistletoe may have gone out of fashion, but mistletoe may regain its status as a symbol of new life and renewal, because cancer researchers are looking into its use in fighting cancer.

This story was originally published December 4, 2016 at 6:15 AM with the headline "Garden Tips: Mistletoe may be cute above door frame, but it’s a parasitic plant."