Under the Mistletoe
A bundle of Viscum album hanging for sale. The European Viscum album has a brighter, yellowish-green appearance compared to the American Mistletoe, Phoradendron leucarpum.
I recently visited the Tübingen Schokoladenfestival— a wintery festival specifically for chocolate! Stands with every flavor and assortment of chocolate line the city center where you can sample or select the sweets— there are even edible chocolate figurines like chocolate violins, high heels, or wrenches. The streets are packed with people, bundled in their winter hats and scarves, sipping on their mugs of warm, thick hot chocolate or steaming, spiced Glühwein. This chocolate festival is specific to Tübingen, and it is a precursor to the annual Christmas market, which similarly take place in most German cities and villages during December. As I was walking towards the chocolate-filled marketplace, I came across a variety of Christmas trees and mistletoe on display for sale. I thought, what a perfect plant to learn more about for the Christmas season!
While there are about 1,300 different species [6],the genera Phoradendron and Viscum are known as “true mistletoes” or “leafy mistletoes”— these are what you imagine when you think of mistletoe. In Europe, the iconic mistletoe, Viscum album, and 130 other Viscum species are widely distributed. Similarly, there are around 240 Phoradendron species in the Americas that are known as American true mistletoes. American true mistletoes can grow on hardwoods or evergreens across the U.S.— there’s even a leafless desert mistletoe found in the southwest! In Pennsylvania, you could come across the Oak or American Mistletoe, Phoradendron leucarpum, as it is the only mistletoe found in the eastern U.S. This species resembles the European Viscum album. While they can have a wide variety of host species, American Mistletoes typically have only one or a few host species within a local area, which suggests that they form populations that are locally adapted and specialized to their host [1].
What do I mean by host species? Well, mistletoes are actually an interesting type of aerial parasitic plant! As hemiparasitic plants, true mistletoes attach to the branches of their host tree and uptake its water and inorganic nutrients, but they also have chlorophyll to perform photosynthesis and produce organic sugars. As obligate parasites, mistletoes require a host plant to develop; although they will weaken the host plant, their aim is not to kill it because they require the host for their own survival [1].
Mistletoe species can look vastly different and have many different host types, but all mistletoes produce berries and are either fully or hemiparasitic; some mistletoes grow on cacti or shrubs, but most have tree hosts and appear as bush-like plants on their host [6]. Trees can become so infected with mistletoe that an otherwise bare deciduous tree can appear full of foliage during the winter months [2]. While mistletoes can exacerbate drought stress and lead to a tree’s total or partial mortality [1], true mistletoe could also be considered a leafy Robin Hood. As they siphon water and nutrients from their host, they also “give back” to other organisms in their habitat. Leafy mistletoes can provide shelter and food for mammals, birds, and even butterflies. Their fallen leaves also return nutrients to the soil. Although they “steal” nutrients from trees, these parasitic plants are ultimately an integrated member of their ecosystem [3].
The plentiful white berries on the branching Viscum album. (Photos by Faith Forry)
As a dioecious plant (having male and female individuals), the sex of a mistletoe plant is indistinguishable until it begins to flower. After pollination, female mistletoes then produce bountiful clusters of small, whitish, single-seed fruit. Although the seed is indigestible, the flesh is nutrient rich and alluring for many birds. Birds have different methods of eating the seeds— thrushes eat the whole fruit, while blackcaps only eat the flesh. Depending on the bird’s behavior, the seeds can be dispersed across greater distances when the bird deposits its feces on a tree, or the bird may wipe its beak directly on the tree as it enjoys the fruit. Either way, once distributed onto a tree, the seed will germinate in the spring forming a non-parasitic seedling on the host branches. Over time, different mistletoe species will develop various sophisticated ways of attaching to the host tree, and after about five years the mature mistletoe plant can also produce flowers and fruit [2].
True mistletoe, with its clustered, white berries and vibrant green, branching leaves, is an iconic feature of Christmas, adorning doorways and inciting affection. However, mistletoe folklore spans across time and the world, beyond only the Christmas season. According to European folklore, mistletoe was thought to be sent to earth from the gods, using a special messenger— the Mistle Thrush bird— which migrates from Africa to Europe, dispersing mistletoe seeds. Since it was sent from the gods, mistletoe was thought to have spiritual and medicinal power. In medieval Europe, Viscum album was used for all sorts of illnesses, and even amulets were worn to ward off illness. These beliefs were shared in Japan, where mistletoe grew on the sacred willow tree. Even Navajos used Areuthobium mistletoe species as medicine— although these are dwarf mistletoes which are classified separately from true mistletoe. English, Japanese, and Indian people also associated mistletoe with fertility, using it to promote conception and aid childbirth [1].
Interestingly, mistletoe is actually poisonous to humans, as phoratoxins are concentrated particularly in its leaves [4,6]. American mistletoe is less toxic than European mistletoe and will likely only cause nausea or vomiting if ingested. European mistletoe, on the other hand, also contains viscotoxins which prevent new cell growth, and this can cause more severe reactions including delirium, central nervous system, kidney, and liver damage, or even death [6]. The extract of European mistletoe is currently being promoted as an injectable cancer treatment in Europe; however, this research is still very limited [5,6]. Mistletoe should generally be considered toxic and be kept out of reach from children and pets.
Mistletoe also had other associations for earlier Europeans. In the first century, Celtic Druids believed the oak tree represented gods, and mistletoe represented people’s dependence on gods [1]. During a special winter solstice ceremony, it is thought that Druid priests would cut mistletoe from an oak tree with a golden sickle; the branches were caught in a cloth, and the sprigs were distributed to the people to hang over their doorways as a protection against lightning, thunder, and other evils [7]. While it’s uncertain how the custom of kissing under the mistletoe began, one possibility is that eighth century Scandinavians associated mistletoe with Frigg, their goddess of love. After Loki tricked her blind son Hoder into shooting his brother Balder with a poisoned mistletoe dart, Frigg’s tears turned the mistletoe’s berries from red to white, bringing her son Balder back from death. Frigg would then kiss anyone who walked underneath the mistletoe as a gratitude for having her son back [1,7]. In some German cultures, mistletoe would be brought into a house to rid it of ghosts and other evil spirits. Overall, mistletoe was thought to bring good fortune, which is why it would be hung over doorways [1].
Perhaps the mistletoe’s general power of good fortune and fertility could bring together two lovers [1]. Kissing under the mistletoe is first found to be associated with Saturnalia, the Roman holiday to honor their god Saturn, and with early marital rites. Then, in England, Christmas mistletoe was burned for good luck or to foretell a woman’s marital future [7]. In the 1800s, the mention of mistletoe in literature by Charles Dickens and Washington Irving expanded upon its popularity in England and America. It was customary that a man could kiss any woman under the mistletoe, and it would bring good luck to accept. However, with each kiss, a berry would be picked, and once the berries were gone, so was the opportunity to kiss [1,4]! Though its uses have evolved over time, the charm of mistletoe remains as a quintessential doorway Christmas decoration.
I hope you have a joyous Christmas season filled with love, laughter, and thanksgiving for the true meaning of the season. If, while you’re baking Christmas cookies, sipping on hot cocoa, or doing some Christmas shopping, you hear a song about mistletoe, I hope you can appreciate the fascinating ecology and folklore surrounding this decorative plant. And if you happen to find yourself under the mistletoe this Christmas season, remember to plant one on your special someone— but don’t eat the berries!
If you found this topic interesting, I’d recommend checking out https://forestpathology.org to learn about other parasitic plants, tree pathogens, and a plethora of forest ailments. If you ever have a blighted tree and you’re unsure what is afflicting it, you’re likely to find some answers there.
Sweet emblem of returning peace,
the heart's full gush and love's release,
Spirits in human fondness flow
and greet the pearly mistletoe.
Oh! Happy tricksome time of mirth,
giv'n to the stars of sky and earth!
May all the best of feeling know,
the custom of the mistletoe.
Married and single, proud and free,
yield to the season, trim with glee:
Time will not stay ... he cheats us so
... A kiss? ... 'tis gone ... the mistletoe.
- The Pickwick Papers, Charles Dickens (1826) [7]
Written by Faith Forry — December 17, 2024
[1] https://forestpathology.org/parasitic-plants/true-mistletoes/
[2] https://herbaria.plants.ox.ac.uk/bol/plants400/profiles/UV/Viscumalbum
[3] https://www.smithsonianmag.com/science-nature/biology-mistletoe-180976601/
[4] https://www.kew.org/read-and-watch/mistletoe-christmas-tradition
[5] https://www.nccih.nih.gov/health/european-mistletoe
[6] https://www.webmd.com/first-aid/mistletoe-poisoning
[7] https://janeausten.co.uk/blogs/home-and-hearth/the-legend-of-the-mistletoe?srsltid=AfmBOooLr18-h5YnCScBMT7C6sm0Mzht3h-jW6_tM1NVpIzcn2pmoBaA
