Mistletoe is Poisonous, Parasitic, and Spread by Poo

Kissing under the mistletoe is a classic part of Christmas romance!

Unfortunately most of us can’t make that special moment happen…

…and many of us just think it’s weird to have to kiss someone if you’re standing under a certain plant.

Don’t worry, fellow Scrooges and Scrooge McDucks, you’re not missing out.  Mistletoe is poisonous, parasitic, and spread by poo.

First, we need to explain what mistletoe is.  In Europe, “mistletoe” usually means Viscum album; in the U.S., “mistletoe” is usually Phoradendron leucarpum.

You can find mistletoes growing high on the branches of other trees.

Both American and European mistletoe belong to the same order of nasty parasitic plants called… wait for it… the Santalales.

Yeah, you can’t make this stuff up.

So why all the smooching?  The European mistletoe has been considered a symbol of fertility at least as far back as Celtic druids in the first century A.D.; the custom of kissing under mistletoe caught on in the 1700s in England.   People were likely inspired by the fact that the plant’s berries persist through the winter.

But the reason the berries persist is that they’re poisonous to most animals!  Mistletoe fruits contain alkaloids and lectins that can cause gastrointestinal distress, a slow heartbeat, and other problems.

Even birds that eat mistletoe berries quickly poop the seeds out… thus spreading new mistletoe and holiday cheer on the branches of nearby host trees.  🌿🐦💩 🌱

That might be a cheerful and festive tale if mistletoe were good for trees.  But in fact, mistletoe is a parasite, sucking water and minerals out of its host!  European mistletoe is missing crucial components of its electron transport chain, leading researchers to conclude that mistletoe steals sugar from its host plants instead of making the energy molecule ATP from scratch.

Because of its vampiric tendencies, mistletoe often damages or kills its host plants.  One of its usual victims is the Scots pine (Pinus sylvestris).  In other words: in the wild, mistletoe can (and does) kill Christmas trees!!

Now, despite the fact that mistletoe is a tree-killing barf-inducing poisonous poo-propagated parasite, there are LITERALLY A HALF DOZEN TV MOVIE ROM-COMS featuring mistletoe!

Plant Humor has taken the liberty of crafting a more accurate film:

Kim is an aspiring romance novelist who has just been dumped by her successful boyfriend. Deciding she needs a change, Kim enrolls in a writing retreat at a snowy Vermont inn shortly before Christmas.  She’s initially irked with her assignment partner Zeke but he starts to grow on her.  Late one night, Kim and Zeke are bantering and eating holiday cookies when they notice they’re standing under the mistletoe.

“Maybe it’s time to write a new ending”, says Zeke, leaning in for the kiss.  Just then, a bird poops on Zeke’s shoulder, depositing dozens of mistletoe seeds.  Zeke lets out a shriek and stumbles backwards into the Christmas tree.

Unfortunately the Christmas tree is weak, having been parasitized by mistletoe; it tumbles down with a crash, narrowly missing Kim and Zeke.  Zeke shakily gulps his eggnog to steady his nerves.  Little does he know that several crushed mistletoe berries had fallen in his drink during the commotion.  The mistletoe-laced ‘nog starts to work its magic on Zeke’s gastrointestinal tract.  Zeke violently throws up all over Kim’s festive sweater.  Kim ends Christmas Eve trying to scrub up the vomit, while mistletoe’s seeds spread far and wide, sowing chaos and indigestion!  ~Roll Credits~

So this holiday, make sure to say what’s really in your heart…

We’re rooting for you, creepy stalker dude!

Sources & Further Reading:

Dobbertin, M., and Rigling, A. (2006). Pine mistletoe (Viscum album ssp. austriacum) contributes to Scots pine (Pinus sylvestris) mortality in the Rhone valley of Switzerland. For. Pathol. 36, 309–322.

Senkler, J., Rugen, N., Eubel, H., Hegermann, J., and Braun, H.-P. (2018). Absence of Complex I Implicates Rearrangement of the Respiratory Chain in European Mistletoe. Curr. Biol. 28, 1606-1613.e4.

Tennakoon, K.U., and Pate, J.S. (1996). Effects of parasitism by a mistletoe on the structure and functioning of branches of its host. Plant Cell Environ. 19, 517–528.

Vidal-Russell, R., and Nickrent, D.L. (2008). The first mistletoes: Origins of aerial parasitism in Santalales. Mol. Phylogenet. Evol. 47, 523–537.

Yule, K.M., Koop, J.A.H., Alexandre, N.M., Johnston, L.R., and Whiteman, N.K. (2016). Population structure of a vector-borne plant parasite. Mol. Ecol. 25, 3332–3343.