Mistletoe Stranger Than Its History?

Jennifer Smith sometimes wonders how mistletoe developed such a mystical, yet romantic reputation. She suspects much of the folklore and legends that “explain” its history and uses may be as rootless as the plant itself.

“How could you possibly decide that putting a poisonous, perennial tree parasite under your pillow would make you dream of the person who’ll become your Prince Charming?” she asked.

But, Smith also believes the facts about mistletoe are interesting enough. In part, her stance may relate to her being a K-State Research and Extension horticulturist. In part, it may relate to mistletoe’s belonging to a small group of semi- (or hemi-) parasitic plants with rather odd living arrangements and reproductive habits.

Oak (tree) mistletoe is the one variety found in Kansas, she said. It only occurs in the southeast corner, where the weather tends to be wetter and warmer than state averages.

Southeast Kansans have yet to celebrate the plant’s presence. In contrast, Oklahoma’s 1893 Territorial Legislature adopted what would become the first state icon – mistletoe, the official state floral emblem.

“If Oklahomans died in winter back then, mistletoe produced the few flowers available to put on the grave,” Smith said. “It was a pioneer thing.”

Much of mistletoe’s success comes down to the fact that its female plants produce sticky seeds, she said. The seeds can adhere to most surfaces and then harden, so they stay in place.

As with peaches, plums and cherries, those seeds are protected inside the plant’s fruit – in this case, mistletoe’s waxy-white berries, Smith said. To germinate and grow, however, mistletoe seeds must end up on a woody plant, not fall to the ground. The female plants approach that feat in widely varying ways. 

Many Americans think of mistletoe as a tree-weakening problem of the South, she said. But, the warmth-loving species has a relative that’s much more dangerous, plus grows well in cooler climates. Known as dwarf mistletoe, this relative is similar, yet has no leaves.

“Dwarf mistletoe varieties infest pines, spruces, firs, and junipers in Colorado, the western states and up into Canada,” Smith said. “Because evergreens never go dormant, their mistletoes are considered more problematic. Dwarf mistletoes are also easier to overlook because they have no leaves and they grow on plants that always do have leaves.”

Rather than relying on animals, the leafless dwarf mistletoe varieties prefer spreading their own seeds. The plants’ berry-like fruits explode, shooting seeds in all directions at almost 60 miles per hour. Naturally, their success depends on where the seeds land, she said.

In contrast, the varieties with leaves mostly prefer hosts that lose their leaves and go dormant each fall. The leafy green mistletoe and its glistening berries become obvious once the trees’ branches are bare.

Leafed varieties disperse seeds via birds that eat the berries. Mistletoe fruits (as well as the stems and leaves) contain toxins that can harm and sometimes kill humans, pets and livestock.

“Birds can’t digest the seeds, though. So, they get rid of those leftovers the next time they deposit droppings on branch tops and other favorable locations,” Smith said. “Perhaps that why the origin of the word ‘mistletoe’ appears to be the Anglo-Saxon words ‘mistel and ‘tan’ -- which together basically mean ‘dung on a twig.’”

Although mistletoe’s seed dispersal can seem chancy, its life as a plant has real benefits, she said.

Mistletoe develops holdfasts – a kind of specialized root – to retain its grip on woody surfaces. The holdfasts grow down into the tree and draw out the water and mineral nutrients the plant needs to survive. Because mistletoe is green and has chlorophyll, however, it takes care of its own food-making photosynthesis.

“Plus, mistletoe is literally outside most plants’ highly competitive world on the ground. It doesn’t have to fight for water, soil minerals or space,” Smith said. “And, even if you break it off, you won’t kill a mistletoe. The half that’s still inside the tree will keep things going.” 

As a hemi-parasite, mistletoe is more likely to weaken than to kill an established deciduous tree, she said. Often, the worst damage it causes is to starve the part of a branch that extends beyond mistletoe holdfasts.

“That can actually allow the mistletoe to have its cake and eat it, too,” Smith said. “The limb loss is a kind of ‘pruning’ that may induce the host plant to produce additional fruit. Typically, though, it will cause the tree to produce twiggy clusters -- called witches’ brooms -- that give the outside of the leaf canopy a sort of overgrown, distorted look.

“To a degree, witches’ brooms make more room for mistletoe to grow. But, they definitely create more shelter for birds -- places where the birds can nest, roost and be available to help with mistletoe’s spread.”

Mistletoe myths and legends can be particularly hazardous for those living outside Europe, Smith warned. (They’re disappearing as forests do, but various varieties of mistletoe grow on every continent except Antarctica.)

Historically, Europe is where ancient peoples have experimented with using mistletoe as a magical, mystical herbal – with mixed results. It’s also where people began flirting with danger, as well as each other, with a winter tradition called “kissing under the mistletoe.” Men collected berries for each kiss "stolen" in this Christmas activity.

Current research is suggesting European mistletoes are more poisonous than the U.S. varieties.

“Evidently, people get into serious trouble with U.S. mistletoe only if they ingest more than they’re likely to eat by accident,” Smith said. “Of course, we still have to be careful with mistletoe around babies and pets. They don’t know when they need to be careful. Besides, size makes a difference in how much of the plant you can consume without developing nausea or diarrhea or something worse.”

Ironically, since the middle of the 20th century, the recorded U.S. mistletoe-related deaths have all had direct ties to its use as an herbal. Two Americans died after drinking a home-brewed mistletoe tea. Another person developed hepatitis after long-term use of an herbal medication that contained mistletoe.

“We simply don’t know enough yet – particularly about U.S. mistletoes – to be doing that kind of self-dosing safely,” Smith said. “But, research is ongoing. Some mistletoe proteins are showing promise, for example, as a possible treatment for breast cancer. Mistletoe just might have a proven medicinal place in our lives within the next decade or two.”