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Mistletoe's darker side

mistletoe with berries
Mistletoes are parasitic plants that take nutrients from trees.

As you kiss under the mistletoe this holiday season, consider the biology of this plant. Parasitic to other plants, mistletoes leech water and nutrients to survive. Shital Poudyal, an Ornamental Horticulture Specialist with USU Extension, said that some mistletoes are hemiparasites, meaning they can produce some of their own food through photosynthesis, while others are holoparasites, relying completely on their host plant.

The type of mistletoe we associate with the winter holidays is American Mistletoe, native to the southern United States and Mexico. There are over 1,300 species of mistletoe worldwide, with 2 species native to Utah.

Sheriden Hansen, an Assistant Professor of Horticulture with USU Extension, said Utah’s mistletoes don’t look like the traditional Christmas decoration.

“They're both dwarf varieties. They're not the type of mistletoe that you pick up, that's leafy,” Hansen said.

Unlike the iconic leafy mistletoe seen on holiday cards, Utah’s mistletoes look more like the junipers and pines that they parasitize. Poudyal said these species of mistletoe are holoparasites, leeching both water and carbon from their hosts.

“They don't have these leaves, rather they have scales, so they can’t photosynthesize as much,” Poudyal said.

While mistletoes don’t immediately kill their host plant, they weaken the tree and can even cause a systemic infection, traveling through the plant to produce growths at different parts.

“It brings a whole new kind of feel to kissing under the mistletoe you know you're kissing under this parasite that's stealing nutrients from a larger tree,” Hansen said.

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Caroline Long is a science reporter at UPR. She is curious about the natural world and passionate about communicating her findings with others. As a PhD student in Biology at Utah State University, she spends most of her time in the lab or at the coyote facility, studying social behavior. In her free time, she enjoys making art, listening to music, and hiking.