It’s hard to imagine a holiday season without Bing Crosby’s Christmas standard I’ll Be Home for Christmas. Originally written from the perspective of a soldier stationed overseas during World War II, his longing for the simple comforts of home and reconnecting with his loved ones at Christmas is almost palpable: “Please have snow and mistletoe and presents by the tree…”
Mistletoe just inexplicably feels familiar. Every December, the evergreen sprigs that spent the offseason hidden in our subconscious are suddenly all around us. Mistletoe is the long-lost acquaintance that we instantly recognize and embrace, yet whose backstory has been lost to us.
“When I talk to people about parasitic plants, I know mistletoe is the one that they’ll immediately recognize even if they don’t really know it’s a parasite,” Virginia Tech plant biologist Jim Westwood tells Popular Science.
A brief history of mistletoe
Author Washington Irving, best known for The Legend of Sleepy Hollow and Rip Van Winkle is often credited with helping popularize the parasitic evergreen shrub in the United States. He wrote about the plant in an 1820 collection of short stories, but the roots of mistletoe go much deeper elsewhere in the world.
Dating back to Ancient Greece and Rome, leafy mistletoe has long excited the imagination. Mistletoe served as a centerpiece of Celtic Rituals and Norse myths, where it bestowed life and fertility and served as an aphrodisiac, a plant of parley, an antidote for poisons, and a means of safe passage to and from Hades. According to The Living Lore, since the plant can thrive in the high branches of its host without soil, “many cultures saw mistletoe as a sacred plant, existing in liminal spaces between life and death, earth and sky, and human and divine.”
In Old Norse mythology, Baldr, the son of the god Odin and the goddess Frigg, was slain with a mistletoe spear. Some interpretations suggest that, “kissing under the mistletoe symbolizes forgiveness, echoing Frigg’s grief and eventual reconciliation with the plant.”
Many early physicians and scientists saw mistletoe as a cure-all for the woes of the world. It was used to treat various diseases and conditions including epilepsy, infertility, and ulcers.
In Pliny’s Natural History, the writer and physician describes the Celtic ritual of oak and mistletoe. High priests dressed in white harvested mistletoe with golden sickles from the branches of sacred oak trees to make an elixir that could counteract any poison and render any barren animal fertile.
“It’s easy to imagine how people become fixated on mistletoe plants,” says Westwood. “It stays green all winter growing in its host tree. It almost seems to have supernatural powers.”
Supernatural or not, mistletoe was so popular throughout the 19th and the early 20th century, that its seasonal availability was tracked and reported by many newspapers. There was little wild mistletoe to be plucked from trees in or around a typical city, so it was often imported from down south where it was a welcome interloper on account of its predictable seasonal payout.
“That’s kind of an interesting thing about mistletoe,” Carolee Bull, a plant pathologist at Penn State and president of The American Phytopathological Society, tells Popular Science “People wanted to manage it because it’s parasitic, but they also wanted it as a product to sell.”
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Mistletoe, the plant parasite
Common or leafy mistletoes (Viscum species in Europe and Phoradendron species in the United States) are evergreen parasitic shrubs. They have small leathery green leaves and white, translucent or red berries depending on the species. Without a perennial woody host plant to support them, mistletoe would quickly die.
However, not all parasitic plants are created equal. Leafy mistletoes are considered hemiparasites. “It’s taking primarily water and nutrients from the tree it’s growing on, but it can make some of its own food because its leaves still contain chlorophyll,” says Westwood. “Because they are green, you wouldn’t necessarily recognize them as parasites.”
Mistletoe plants are poisonous as well. They contain one or more peptide toxins— particularly concentrated in the leaves and stems—capable of causing heart and gastrointestinal issues in various animals including humans. They also have been reported to cause dermatitis. European Viscum species are considered more toxic due to the presence of viscumin, a toxin similar to ricin from castor bean that is not present in their American Phoradendron counterparts. Despite their deadly reputation, most reported accidental ingestions (e.g. a few leaves or berries), with the exception of excessive, concentrated herbal use, such as brewing mistletoe in tea, have not been fatal.
In the 13th century, German Dominican friar and scientist Albertus Magnus, was among the first to formally recognize and document European leafy mistletoe (Viscum album) as a plant parasite. Magnus even went as far to recommend pruning infected branches as a form of control, helping lay the foundation for the field of plant pathology.
“So much of the work we do as plant pathologists is microscopic,” says Bull. “We often use techniques that can tell us whether or not an organism is there. And mistletoe is one of the few organisms that we don’t have to do that for. It’s a really charismatic plant pathogen.”
Parasitism may seem like a strange lifestyle for a plant, but around 4,000 plants (roughly 1 percent of all known plants) live as parasites. Some like mistletoe are partially dependent on their host, while others (called holoparasites) rely on their hosts for everything.
“It’s a good lifestyle to steal your food rather than make it yourself,” says Westwood.
Parasitic evergreens and where to find them
Outside of your local holiday market, finding real leafy mistletoe is easier than you might think.
“It’s the perfect plant for roadside botany,” says Bull, referring to the practice of identifying plants without leaving your car. Their conspicuous position high up in the branches of their tree hosts following leaf fall makes them almost impossible to ignore.
In the U.S. alone, more than a dozen species of Phorodendron are found in over 35 states, and live abundantly across the entire southeast, southwest, and Pacific Northwest. Even if you find yourself geographically removed from the places where leafy mistletoe thrives, you can still find another less conspicuous type of mistletoe called dwarf mistletoe (Arceuthobium species), which parasitizes the branches of conifer trees.
There are even leafy mistletoe “hot spots” since their sticky berries are spread primarily by the birds that eat them. Clearly, the health risks associated with mistletoe ingestion don’t apply to birds. In fact, the word mistletoe literally translates to “dung on a twig,” an accurate reference to how it spreads. Birds eat mistletoe berries in winter, spreading the seeds in their fruit-rich droppings. Their seeds adhere to random tree branches due to a sticky viscin on the seed coat that even survives its journey through a bird’s digestive system. It will remain there until the following spring when it germinates and enters its host to begin its life as a parasite.
So the next time you’re driving and The Jackson 5’s I saw Mommy Kissing Santa Claus or Justin Bieber’s Mistletoe begins to play, remember that mistletoe isn’t just some generic seasonal evergreen or Victorian era kissing contraption. It’s an ecologically important parasitic plant with both ancient and contemporary roots that’s here to stay.
In The History of Every Thing, Popular Science uncovers the hidden stories and surprising origins behind the things we use (or eat) every day.
