What is Mistletoe?

What is Mistletoe?

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Mistletoe berries from the UK (Photo: Wiki Commons).

The Irony of Mistletoe As the "Kissing Plant"

Evergreens have long been a symbol of winter and holiday celebrations around the new year. Evergreen boughs are brought inside, holly trees and their red berries seem festive, and even Christmas ferns are used for decorations. There's one evergreen that has especially stood out over the years, and that's mistletoe. Today's post is all about this unique plant, and why it's ironic that this particular evergreen is associated with lovers and "kissing under the mistletoe" traditions.

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Mistletoe clump in a birch tree (Photo: Wiki Commons).

What is mistletoe?

Well, the term mistletoe is used as a catch-all (like "pine tree") for around 1,300 mistletoe species that occur around the world. They are plants that are in the order Santalales (Santa-la-less). I find it funny that the order name has the word Santa and la-les in it. Here in North America there are 30 some odd species. The most common species in the US is the oak or eastern mistletoe (Phoradendron leucarpum). It is the "surrogate" to the mistletoe that is used most commonly in Europe.

So here's the irony,  all mistletoe plants are hemi-parasitic (this makes it sound like a truck with a hemi-engine, but it's something else). Hemiparasitic means that the plant has leaves with chlorophyll and it can make its own food through photosynthesis, but it needs other plants for water, nutrients, and minerals. This is why they live in the bough of trees and on other plants. It's quite literally a half-parasite. Wait....it gets weirder.

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A clump of mistletoe growing from the bark of a tree (Photo: Wiki Commons).

What's In A Name?

The term mistletoe comes from the Anglo-Saxon mistrel which means "dung" or "poop" and the word tan which means "twig." Mistletoe's name literally translates into "poop-on-a-twig."  American mistletoe is in the genus Phoradendron, which is also a fun Greek name meaning "thief of the tree." Thieves and poop, feeling romantic yet?

To be fair, "mistrels" were also singers and they did sing love songs, so mistrel-toe isn't a far stretch. It was also used in ceremonies to cure infertility (results pending). In German the term "mistle" in verb form means "misty raining" (sort of like our mizzle), which does apply to the seeds, and on that note....

The Seedy Truth

Mistletoe is a green plant that produce a white drupe (bunch) of berries. These white inner fruit and seeds are quite sticky, and birds love them. Birds eat the seeds and then poop them on the twigs of trees (poop-on-a-twig), or carry the sticky seeds on their beaks and feet to other trees. The seeds germinate just fine after passing through a bird's digestive tract, and they may even need the rough stones from the bird's crop to scuff them to stimulate germination. There is even one species of mistletoe whose sticky berries explode (at nearly 60 mph) and eject seeds up to 35 feet away.  Many creatures eat the poop-on-a-twig berries, including deer, elk, porcupines, squirrels, chipmunks, robins, doves, bluebirds, and chickadees. But be careful! They are very poisonous to humans, cats, and dogs, which is why I suggest caution with mistletoe bouquets around children and pets at Christmas.  Ah, true love, poisonous berries, poop and projectile seeds!  Makes the season bright, right?

What holiday would be complete without a video of a mistletoe bird, also known as a mistletoe flowerpecker, from Australia (and New Guinea) eating the seeds of mistletoe and then "gardening."

Parasitization

This gets us to parasitization. When the mistletoe's seeds land on a suitable host (usually fruit trees like apples and cherries or oak trees, junipers and such) the roots of the seed penetrate through the tree's twigs or branches and start to draw nutrients and water. As the mistletoe matures it grows into a thick green bunch (often roundish), and up to about the size of a tire. These bunches are sometimes called "witches brooms" and can weigh up to 50 pounds.

Some species of mistletoe start off as semi-parasitic and eventually give up photosynthesis all together and become complete parasites. These guys then just stop pretending to photosynthesize, turn yellow, and play sippy-straw on the tree their rest of their lives.

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Mistletoe can grow in large damaging clumps in trees (Photo: Wiki Commons).

Mistletoe, or the half-parasite-poop-on-a-twig plant, can do a great deal of damage to a tree, especially if there are lots of bunches in one canopy. Trees infested with mistletoe can eventually die. It's not all bad though. If a tree dies from mistletoe parasitization then it can become a brood tree, full of useful cavities and insects, for nesting birds and mammals and insectivores that eat the insects from inside the dead tree. Despite the ecological advantages, many home owners choose to cut mistletoe infected limbs off and dispose of them.

But wait, before you go chopping off the poop-on-a-twig laden limbs off, consider this, some species of butterfly rely on mistletoe for laying their eggs, including the great purple hairstreak, Johnson's hairstreak, and thicket hairstreak. Because mistletoe is evergreen, it also blooms first in Spring, offering some of the season's first nectar and flowers to bees and pollinators. Birds also find mistletoe to be a great place to nest. In studies by the USGS it was shown that 43% of Mexican spotted owl nests were affiliated with mistletoe clumps. Nearly 64% of all Copper's hawk nests in Oregon were also associated with mistletoe clumps. Other nesting species that included mistletoe were long-eared owls, great gray owls, sharp shinned hawks, goshawks, gray jos, red crossbills, house wrens, pygmy nut hatches, chipping sparrows, Cassin's finches, and pine siskins. The evergreen clumps provide cover and hiding year round.

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A clump of mistletoe growing in a tree (Photo: Wiki Commons).

Medical Poop-On-A-Twig

Mistletoe also has medical applications that make it valuable. Most recently it has been used in Europe as a therapy for cancer. It has been found that mistletoe extracts, or lectin, inhibit the growth of tumor cell lines. Essentially what the lectin does is cause apoptosis (a fun word meaning cell death) in cancer cells. Research also shows that African mistletoe, which has been used in Nigerian folk medicine to treat diabetes, does reduce diabetes in lab rats, which shows promise for humans.

I'm not going to go into the mythic history of the kissing plant here, I think the natural history is strange (but neat) enough. If you'd like to read more check out the article from the Smithsonian (click here). 

Regardless of whether you're celebrate Christmas or other holidays, you've doubtless heard of mistletoe and the tradition of kissing under it. Just be careful, if you're using live mistletoe branches or bunches, you may just find yourself under the poop-on-a-twig or near exploding berries!