Mistletoe: The Poisonous Plant We Hang At Christmas

For centuries, people have hung mistletoe as an expression of love and romance. But unfortunately, the plant doesn’t harbor the same feelings. Why?  Because mistletoe contains a Christmas cocktail of toxins that when ingested can be harmful to humans and pets. I’d advise keeping it out of reach if you’re planning to make it part of your holiday décor.

WHAT MISTLETOE IS

For all its romantic associations, mistletoe is no loving plant. In fact, it is parasitic. That means it specializes in attaching itself to the branches of a tree or shrub and penetrating it to steal water and other nutrients.

And while its deep green, ball-like form adds a touch of ‘life’ to bare branches, once mistletoe gets its roots into a plant it starts to destroy it. This often requires the removal of all infested limbs and in some cases entire trees in which there are large-scale invasions.

Attractive but parasitic bright green clusters of European mistletoe

IT LIKES TO SPREAD

As if that weren’t bad enough, its seeds are also easily dispersed. Those pretty white berries that add a festive touch to the sprig? Birds love them. As they’re carried away, the berries’ sticky pulp drops onto the upper branches of shrubs and trees, sowing mistletoe on other species.

All told, it can take up to two years for a mistletoe to fully develop within its host. Once firmly rooted, it sends out aerial shoots that weaken and distort the plant. Sometimes it even kills it.

WHAT HAPPENS IF I EAT MISTLETOE?

There are two main species of mistletoe, Viscum album (European or Common mistletoe) and Phoradendron (American or Oak mistletoe). Both contain a mix of toxic compounds in their stems, leaves and berries that, if ingested, can be harmful to humans and pets.

However, of the two, Viscum album is the more toxic. Its pairs of smooth, oval shaped leaves and clusters of sticky white berries contain a mix of chemicals that include poisonous amounts of the alkaloid tyramine. Tyramine can cause stomach upset, nausea and vomiting, blurred vision, blood pressure changes and in rare cases even death.

The oval leaves and white berries of Viscum album

Not to worry (too much), though. In North America, Viscum album is a rarity unless it has been purposely transplanted to your area. Instead, our own native species, Phoradendron, populates our forests.

Unlike the European species, American mistletoe has shorter and broader leaves and larger clusters of white berries. It also secretes a toxin, in this case phoratoxin, that causes the same symptoms as tyramine. But happily, it’s to a lesser degree.

The paddle-shaped leaves of Phoradendron

In fact, although until recently American mistletoe was widely considered to be as poisonous as the European species, downing a few berries is likely to lead to no more than a stomachache. According to the National Capital Poison Center’s recent studies describing American mistletoe exposures (mainly by young children at Christmas), you’d have to eat a whole lot of berries to experience these reactions. The vast majority of patients who ate parts of the plant had no symptoms. Moreover, there were no fatalities, even among those who had swallowed mistletoe on purpose.

POISONING IN DOGS AND CATS

When it comes to pets, small amounts of mistletoe most likely will cause no more than mild gastrointestinal distress. However, if your cat or dog accidentally consumes large amounts of the plant, it could lead to abnormal heart rate, collapse or even seizures. If you suspect your pet has eaten mistletoe, contact your veterinarian or Pet Poison Helpline for treatment recommendations.

Mistletoe is most harmful to small children and pets/Photo credit: Michael Pettigrew

MISTLETOE AS MEDICINE

On a good note, perhaps due to its toxicity, Viscum album has been used by herbalists as medicine for centuries. This includes using it to improve circulatory and respiratory problems and to treat a variety of conditions including seizures, hypertension, headaches and arthritis. More recently, mistletoe extract has shown promise in stimulating the immune system in some limited laboratory studies. Today in Europe it is also being used as a cancer treatment.

(Although the United States FDA has not approved mistletoe as a treatment for cancer or any other medical condition, it is nonetheless being studied in clinical trials.)

Mistletoe is currently being harvested in Europe for its cancer-fighting properties

THE TAKE-AWAY

Used safely, mistletoe may do a lot more for humankind than just providing a romantic canopy. As we learn more and more about what plants can do, mistletoe’s powerful medicinal qualities are something to celebrate in addition to its decorative properties. Something to think about next time someone reaches in for a kiss under its branches.

 

 

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