Every holiday season, millions of people bring a tree-killing parasite into their homes that could potentially make them and their pets sick.
Most people who hang mistletoe probably think of it as a festive decoration under which couples kiss, but entomologists and botanists warn it’s far from harmless.
Mistletoe is actually a hemiparasite, meaning it attaches to host trees with root-like structures to siphon water and nutrients. Despite its cheerful backstory and associations with fertility and rebirth, entomologist Bill Reynolds calls mistletoe the ‘thief of the tree.’
It cannot grow in soil or pots, but survives only by draining its host, sometimes damaging or even killing the tree. The plant grows in round clusters along branches, keeping its leaves green through winter long after the host tree has lost its foliage.
Though it may look magical, its parasitic process is remarkably ingenious and potentially dangerous if ingested.
The holiday kissing plant is also mildly toxic. If it’s left where children or pets can eat it, it can cause stomach pain, nausea, vomiting, and diarrhea.
Eating as few as five berries or leaves from a mistletoe plant could be enough to trigger these gastrointestinal symptoms in people.
Meanwhile, the ASPCA has listed mistletoe as toxic and recommends contacting a veterinarian if dogs or cats get hold of the parasitic plant
The tradition of kissing under the mistletoe dates back to the 18th century in Victorian England (Stock Image
Mistletoe, which is a hemiparasite, grows in round clusters, looking like it is sprouting magically from tree branches (Stock Image)
Although mistletoe can be surprisingly problematic, its appearance during the holiday season dates back to 18th century England.
People started kissing under the mistletoe, with Victorians popularizing the tradition of a seasonal kiss and then spreading it to the US in the 19th century.
However, ancient Greeks and Romans used the berries for various applications, such as trapping birds and skin ulcer ointment.
Mistletoe was also revered as sacred by the Celtic Druids.
In 1820, Washington Irving wrote that each berry on the plucked mistletoe represented a kiss that a young man is allowed to bestow on a young woman, and ‘when the berries are all plucked the privilege ceases.’
Reynolds told Our State that being only a hemiparasite and not a full-blown parasite, mistletoe does gain some of what it needs to survive through self-sustaining processes like photosynthesis.
The presence of mistletoe is not all negative, as other species can thrive off of it, Reynolds explained.
Birds such as robins, bluebirds, chickadees, nuthatches, pine siskins, pigeons, and mourning doves nest in mistletoe, eating the fruit and spreading the parasite to other nearby trees. Even owls nest in the leafy bushes of mistletoe.
Mistletoe sucks water and nutrients from the trees it grows on, growing white berries that birds carry to neighboring trees (Stock Image)
‘If you look at all of that green, it kind of looks like a dense, bushy cloud in the tree. Have you ever seen an airplane vanish for a second in a cloud? Well, birds use mistletoe like that to vanish from predators. It’s often covered for many bird species,’ the botanist added.
‘If you see a lot of mistletoe in a forest, you can guess correctly that there’s a healthy bird population.’
Mistletoe also feeds other woodland creatures, such as chipmunks, squirrels, and deer.
Reynolds noted that while mistletoe may weaken trees, it rarely kills them, but the topic of how much harm it causes is still up for debate among plant experts.
Recent research in a survey of urban forests in seven western Oregon cities found little connection between mistletoe infestation and negative health outcomes for the trees it was infesting.
Professor emeritus Dave Shaw, an OSU Extension Service forest health specialist, examined the occurrence of western oak mistletoe in city forests to learn about mistletoe hosts and gain insight into mistletoe management.
Common from Baja California to the northern Willamette Valley of Oregon, western oak mistletoe is one of the more than 1,400 species of mistletoe growing around the globe.
‘Western oak mistletoe is probably a benefit to wildlife in urban forests,’ Shaw said in a university release. ‘On the other hand, there is the potential for negative impacts on amenity trees, which is why it’s important for urban forest managers to have assessments of mistletoe host range, both for future tree planting decisions and managing current tree populations.’
