OPENING
Welcome to Episode 39 of The STEM Sessions Podcast, published on December 27, 2026. This is the podcast that says it’s OK to do your own research on STEM topics even if you don’t have any fancy credentials. I am your host, Cody Colborn.
INTRODUCTION
Here’s another episode based on the research I did for my Winter Solstice hikes at Socal Science Hikes – which were incredibly fun, by the way
- Check us out on Meetup if you’re in southern california
One of the topics I shared was mistletoe and the tradition of kissing under said plant
- First part is straightforward discussion of local botany and the science of mistletoe
- Second part is about the origin of the tradition of kissing under mistletoe
A theme of my hike was the crossover between winter solstice traditions and science or natural history
- Assumed the story of mistletoe would be a great example to start off the hike
- Striking visuals of large green balls of mistletoe in our leafless western sycamores
- And I was certain the tradition must go back quite a ways in history; perhaps Roman or Greek, perhaps Gaelic
Turns out, my assumption was wrong, but I had to sift through a lot of internet garbage to figure it out
This is The STEM Sessions Podcast Episode 39 – Mistletoe: The Plant and the Meme
MAIN BODY
While walking through parks and down trails here in southern california, you’ll often encounter large balls of green leafs in the upper branches of trees like western sycamores
- Most obvious during the fall and winter when the tree has gone dormant and lost its leafs
- Green ball really stands out then
- Most people probably don’t pay attention to the sight, or they do but they don’t know what they’re looking at
- But what we’re seeing is big balls of mistletoe
This isn’t technically the mistletoe we think of when we think of Chistmas
- That is European mistletoe, scientific name Viscum album
- It grows throughout Europe and is the only species in Britain, which is where it became popularly linked to the holiday season
North American mistletoe is in a different genus, the genus Phoradendron, and over 30 species are on the continent
- Incidentally, depending on how you categorize, there are up to 1500 species of mistletoe worldwide, every continent but Antarctica
- In California, we have about ten species found in deserts to oakwoodlands to conifer forests
- Species you’re most likely to encounter in the non-desert areas of southern california is big-leaf mistletoe, scientific name Phoradendron macrophyllum – this species is also found across the western US
Parasitic plant which attaches itself to a tree or shrub
- Connects to host plant using a connective appendage called a haustorium, through which it steals water and nutrients
- Technically speaking, mistletoe could kill its host plant by stealing too many resources, but I’ve never seen a tree with mistletoe on it look sick or dying on my hikes
- Granted, that could be a big case of survivorship bias
- But it makes logical sense – mistletoe can’t move, so why kill the plant that’s keeping you alive?
- This isn’t a parasitic situation like a wasp laying its eggs on a caterpillar which is then used as food after hatching – those insects eventually leave so they don’t care if the host dies
Also, mistletoe leafs are green, and they’re green year-round
- Green indicates the presence of chlorophyll, which means mistletoe is capable of making its own food via photosynthesis
- So technically, hemi- or half-parasitic
- How much energy is makes from photosynthesis versus from the host depends on the species and location
You should never consume, or touch for that matter, any plant you can’t identify with 100% certainty
- Mistletoe is no exception as it contains phoratoxin, a chemical that can cause gastrointestinal issues when consumed
- Toxin is found in all parts of the plant including the white berries, the same berries that make it an appealing winter holiday decoration
- While toxic to humans and pets, mistletoe is a valuable source of food in winter for birds and mammals such as deer, squirrels, porcupines, bluebirds, robins, doves
- Host plant to three species of butterfly in North America
While mistletoe is considered generally toxic, there is some nuance to the statement
- American mistletoe – genus Phoradendrum – may be significantly less toxic than European mistletoe – genus Viscum
- A paper in the American Journal of Emergency Medicine from 1997 looked at the outcomes of over 1700 exposures and concluded “accidental ingestion of American mistletoe is not associated with profound toxicity”
- Other poison control centers warn against only minor irritation
- ASPCA considers American mistletoe toxic to dogs, cats, and horses, with clinical signs of omiting, diarrhea, low blood pressure, difficulty breathing, low heart rate
- So better safe than sorry
As far as dispersal goes, most mistletoe is spread via birds
- Birds eat the berries, and defecate the seeds on the branch of another tree
- Seeds are also sticky and adhere themselves to the bird’s beak
- The bird then wipes its beak on a branch to dislodge the seeds, which then stick to the branch and propagate a new plant
- Seed dispersal via animal is call zoochory
A few mistletoe species have evolved a secondary means of spreading seeds – ballistic dispersal, also called ballochory
- Hydrostatic pressure builds within the berries, eventually causing the berry to explode and projecting the seed at velocities upwards of 50 miles per hour
- Often, there is enough kinetic energy for the seeds to reach neighboring trees
- Perhaps this is to improve the chances of the host plant not becoming overtaxed with too many mistletoe plants
Moving on to the holiday lore of mistletoe, if you do an internet search for the origin of the kissing under the mistletoe tradition, the first batch of results will agree the tradition is linked to the old Norse stories about the death of Baldr
- I just opened a search engine and typed in “what is the origin of the kissing under mistletoe tradition”
- AI overview and many of the top results point to the Baldr stories
- Many of these sites have a reputation for trustworthiness
The BBC states: Ancient Norwegian and Scandinavian tales agree that mistletoe has meanings of love and friendship. It is said that the mistletoe’s white berries are tears that the goddess of love called Frigg cried for her son Baldr, and that she announced that mistletoe should be a plant of love.
History.com states: when the god Odin’s son Baldur was prophesied to die, his mother Frigg, the goddess of love, went to all the animals and plants of the natural world to secure an oath that they would not harm him. But Frigg neglected to consult with the unassuming mistletoe, so the scheming god Loki made an arrow from the plant and saw that it was used to kill the otherwise invincible Baldur. According to one sunnier version of the myth, the gods were able to resurrect Baldur from the dead. Delighted, Frigg then declared mistletoe a symbol of love and vowed to plant a kiss on all those who passed beneath it.
Smithsonian Magazine states: In Norse myth, the god Balder is mistakenly killed by an arrow of mistletoe—after which the plant becomes synonymous with his grieving mother’s undying love.
Almanac.com states: The kissing tradition dates back to ancient Norse mythology. According to legend, the goddess Frigga declared mistletoe a symbol of love after it was used to harm her son Balder. From then on, anyone standing beneath the mistletoe was to receive a kiss of peace and affection.
Livescience states: he plant was sacred to Frigga, the goddess of love, but Loki, commonly known as the god of mischief, shot Frigga’s son with a spear or, in some tellings, an arrow carved from mistletoe. Frigga revived her son under the mistletoe tree and decreed that anyone who stands under the mistletoe tree deserves not only protection from death, but also a kiss.
NPR states: In some later versions of the story, Frigg’s tears over her son’s death become mistletoe berries, symbolizing her love
- Though to NPR’s credit, it doesn’t directly link the kissing tradition
And that’s just to cite a few of them
Death of Baldr is a real story
- It appears in both the Prose Edda and the Poetic Edda, which are as close to primary sources for Norse mythology as we have
- Mistletoe plays a major role, but it has nothing to do with love and kissing
- That part simply is not in the text
- Time magazine states: Baldur’s death involves mistletoe, but it’s got nothing to do with kissing or Christmas
Baldr was the son of Freya and Odin
- He was everyone’s favorite
- When he was prophecized to die, Odin traveled to hell to speak to a witch who was ultimately not much help
- Freya more successful as she secured an oath not to harm Baldr from everything in the world: people, animals, plants, rocks, rivers, everything
Feeling relief, family and friends started a past time of hurling different objects at Baldr to find out if he was truly invulnerable
- Baldr, boiling over with confidence, was a willing participant
Loki, always the antagonist to keep the plot moving forward, disguised himself as a servant woman and got Freya to admit she got an oath from everything but this small tree called mistletoe
- It was small enough that it could surely cause no harm, so she didn’t pursue an oath
- Loki finds the mistletoe and fashions a wand or small spear from its branch
- During the next session of let’s throw things at Baldr and see if it hurts him, Loki tricks Baldr’s brother into hurling the spear of mistletoe, which impales Baldr, killing him
The version in the Poetic Edda is mostly the verbal sparring between the between Odin and the witch in Hell
- While a fun read, if you enjoy Old Norse poetry, it doesn’t provide any additional information
- If you want to read it for yourself, I recommend the Jackson Crawford’s “The Poetic Edda: Expanded Second Edition” that was just published
Freya didn’t bless mistletoe, nor is she a goddess of love
- Norse gods didn’t have those titles – they were more personality archetypes
- Freya’s tears didn’t become the white berries of the mistletoe plant
- She didn’t vow to kiss and bless those who found themselves under mistletoe
Modern pagans made that up in order to fabricate a connection to the old ways
- And when enough sites and youtube videos and instagram stories repeat the same fabrication, the internet reports it as fact
- When questioned, they’ll say not all poems were recorded, so we can’t say what they believe isn’t true
We are almost certainly missing poems from that time period – potentially dozens if not hundreds
- But a few legitimate old Norse scholars believe it’s more likely there is a missing poem in which the gods punished mistletoe for its role in Baldr’s death by changing it from a tree to the parasitic plant it is today
- That ending is a better thematic fit to Old Norse poetry in general
So what’s the real origin of the kissing under the mistletoe tradition at Christmas?
Time magazine published a good write-up in 2018
- In 1719 and 1720 John Colbatch, an English apothecary and physician, wrote two books on mistletoe
- He included an entire chapter on mistletoe superstitions and customs, but mentions nothing about kissing under it
- Earliest evidence is in a song 1784 in England
- So its most likely the tradition began sometime between 1721 and 1783, so let’s call it the mid 1700s
- In 1820, American author Washington Irving wrote about the tradition after visiting England, and that seemed to accelerate its increase in popularity
So, let’s imagine a party in mid-1700s England
- Party is attended by socially conservative people who maintain certain properness in public
- A young lad, who perhaps has consumed a bit of liquid courage, is attract to a young lady across the room
- Looking for a way to break the ice, he notices she is standing under mistletoe – a common holiday decoraction with its green leaves and festive white berries
- He approaches with fake confidences and says “m’lady, I see you’re standing under mistletoe. Did you know there is an ancient Gaelic tradition that says if two people are standing under mistletoe they must share a kiss lest misfortune fall upon them?”
- The young lady, excited by his brashness, replies “good sir, I am a proper lady and would never engage in such public behavior but if tradition says we must…”
- The young lad bragged to his friends, the young lady swooned to her friends, and the rest is history
OUTRO AND CREDITS
Thank you for listening to this episode of The STEM Sessions Podcast – a podcast researched, written, and produced by Cody Colborn.
This episode’s music is titled “Void to the World” and was composed by Alexander Nakarad and can be found on pixabay.com.
The shownotes and transcript can be found at thestemsessions.com, which is also the best place to provide feedback, corrections, and value for value support.
Remember, doing your own critical research will always be to your benefit, and any pundit or scientist that tells you “just trust me, bro” or scolds you for fact checking and questioning isn’t offering true education.
So until the next one, keeping learning.
REFERENCES
https://pubmed.ncbi.nlm.nih.gov/9270395
https://www.history.com/articles/why-do-we-kiss-under-the-mistletoe
https://www.ambius.com/resources/blog/holiday/the-curious-kisstory-of-mistletoe
https://www.smithsonianmag.com/history/how-mistletoe-became-christmas-kissing-tradition-180985450
https://www.almanac.com/why-do-we-kiss-under-mistletoe
https://www.bbc.co.uk/newsround/16164453
https://www.livescience.com/32901-why-we-kiss-under-mistletoe.html
https://www.npr.org/2025/12/17/nx-s1-5641015/mistletoe-dung-manure-etymology