This holiday season, you might be hoping to catch someone under the mistletoe – or it just might be an prospect you’d like to avoid. The association of mistletoe with kisses and Christmas in the Western world dates back to the 19th century, but it has been linked to romance and fertility since ancient times.
“Mistletoe is actually an evergreen plant,” said Marcos A. Caraballo-Ortiz, an associate botany researcher at the Smithsonian National Museum of Natural History who studies Caribbean island mistletoe. This persistent status, combined with the fact that it retains its fruit in winter, has made mistletoe a symbol of fertility and vitality.
To celebrate the holidays, Caraballo-Ortiz shared some other fun facts you might not know about the plant behind the tradition.
Mistletoes are parasites
You read that right – all mistletoe species are pests. But it’s a bit more complicated than Hollywood’s portrayal of parasitism. Mistletoes are specifically known as hemiparasites, a term for a plant that gets some or all of the nutrients it needs from another living plant, Caraballo-Ortiz explained. In the case of a mistletoe, it attaches to the branches of a woody tree or shrub and siphons water and food from the host.
But guises are not incapable of fending for themselves. “They can photosynthesize” early in their life cycle when they first attach themselves to their host tree, he explained. And mistletoes generally do not kill their host. Sometimes the host plant will experience growth retardation as a result of the uninvited guest. âI’ve seen trees that have branches with so much mistletoe on them, the branch can die,â Caraballo-Ortiz said. “But some of them are not noticed on the host at all.”
They don’t grow out of the ground
Due to their parasitic nature, mistletoes never touch the ground. âThey are not touching the ground,â Caraballo-Ortiz said. Instead, when a mistletoe seed lands on a potential host plant, it âhooks upâ and begins to germinate. âTheir fruit is coated with a sticky substance called viscin,â Caraballo-Ortiz explained. “It’s like a fiber that allows the seed to attach itself to the branches of trees.” The seed uses its own photosynthetic powers to produce a hypocotyl, or stem, which comes out and triggers the growth of mistletoe. It then forms a structure called a haustorium, which acts like a root by burrowing into the host branch and carrying water and nutrients from the host to the parasite.
Some mistletoe spread their seeds by exploding, while others depend on birds
So how do mistletoes manage to deposit their seeds on distant tree branches? Some species take seeds from their fruits by increasing the water pressure in their berries and exploding. âIt’s really cool – they can go really long distances,â Caraballo-Ortiz said, in some cases up to 20 feet and at speeds of up to 30 miles per hour.
But many mistletoes, including most of the tropical species studied by Caraballo-Ortiz, are greatly helped by birds. Many birds choose to feed on mistletoe berries, which contain the seeds of the plant. âBirds really love them because they have special sugars and different colors and textures,â Caraballo-Ortiz said of the fruit. “And it is often the only fruit available in winter in many cases.” As the birds fly from branch to branch, they deposit the seeds in their poo. The sticky viscin fixes the seeds to the branch, leaving them ready to start germinating and burrow into a new host tree.
Some mistletoe eat other mistletoe
Most mistletoes are adapted to use trees as a parasitic host. But some mistletoe go further and parasitize other mistletoes. It is not uncommon for birds to scatter the seeds of one mistletoe while they feed on the fruits of another mistletoe. Because mistletoes are susceptible to clinging to any plant, some species have adapted to using these secondary mistletoes as a host. “The birds have constantly thrown seeds at other mistletoes,” Caraballo-Ortiz explained, “so they took advantage of it.”
In these cases, you may find a mistletoe hanging from a mistletoe hanging from a tree, stacked in a sort of parasitic plant chain. These mistletoes have become what is called a hyperparasite: a parasite that parasitizes another parasite. The hyperparasite draws food from the first mistletoe, which in turn siphons nutrients from the tree.
Mistletoe grows almost everywhere on Earth
While mistletoe is associated with the holiday season and the cold in America, there are over a thousand known mistletoe species that grow all over the world. âYou can find them almost anywhere except in extreme environments,â Caraballo-Ortiz said. “But even some of them are suitable for very cold places like Siberia or northern Canada.” These mistletoes have special adaptations that help them tolerate cold weather, while other species are adapted to survive in dry conditions. âAs long as they have a host, they can find a way,â he said.
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