Why do we kiss underneath the mistletoe?

The history of mistletoe, which can be traced back to the ancient Greeks, is long, strange, and full of contradictions. Certain varieties are poisonous, for starters, and ingesting their toxic white berries has been known to cause a host of stomach problems (poison control centers often send out "holiday safety" fliers every year). Yet Hippocrates used other types of mistletoe to treat menstrual pains, and through the centuries it's has been enlisted to fight leprosy, infertility, epilepsy, and even cancer. (Recent research suggests an extract might even help terminate colon cancer cells.)

Then there's the plant's semi-parasitic nature. Mistletoe, a relative of sandalwood, attaches itself onto other trees to steal its host's water and nutrients. Unlike sandalwood, however, mistletoe seeds are dispersed by berry-eating birds, which allows the plant to grow on branches high above the shade, freeloading on other trees' sunlight.

Why, then, do we kiss each other under bunches of the devious, toxic plant every Christmas?

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Some say mistletoe is a symbol of virility [PDF]. According to Smithsonian Magazine, its seeds are coated in a semen-like substance that allows them to stick to tree branches once dispersed by birds — allowing a new mistletoe plant to dig into the host tree and begin to take shape. That's why we hold one another close underneath it.

Another explanation says that early Christians integrated mistletoe into their celebrations as the religion spread across third-century Europe. The rationale predates the early Christians and goes back to the Norse god Baldur — second son of Odin, god of truth and light — who was so beloved by the other gods that they sought to protect him from all the dangers of the world. His mother, the goddess Frigg, "took an oath from fire and water, iron and all metals, stones and earth, from trees, sicknesses and poisons, and from all four-footed beasts, birds and creeping things, that they would not hurt Baldur." And thus the beautiful god was deemed invincible. What does this have to do with mistletoe? Bear with us...

At a large gathering soon after, stones, arrows, and flame were all flung at Baldur to test his might. Nothing worked, and he walked away unscathed. Jealous of Baldur's new powers, the mischievous Loki set out to find the one thing on Earth that might be able to hurt him. He found that the goddess Frigg forgot to ask mistletoe — tiny and forgotten — not to harm her beloved son. In the end, a dart fashioned from the little plant was used to murder Baldur in front of all the other gods who loved him so dearly.

Frigg, of course, was devastated. Steve Whysall at the Vancouver Sun explains that the tears of Baldur's mother became the berries of the plant, and it was decreed that "mistletoe would never again be used as a weapon and that she would place a kiss on anyone who passed under it."

And thus we hang mistletoe underneath our doorways come the holidays — so that we never overlook it again.