Mistletoe is a staple of holiday decorating, and we all know what to do when we find ourselves standing beneath it. But how did this plant become associated with holiday celebrations? And why are we expected to pucker up in its presence?

Read on to learn a few things you might not know about this traditional holiday plant.

1. It has a long history.

Mistletoe plays a prominent role in Norse mythology. According to legend, Frigga — the goddess of love and marriage — had a son named Balder who was killed with an arrow of mistletoe. Heartbroken, Frigga wept, and her tears became the mistletoe’s white berries, which brought Balder back to life. Frigga was so overjoyed that she blessed the plant and said that whoever stood beneath it would be kissed. Thus, the plant became a symbol of love and peace.

The Druids also thought mistletoe was special. Because it remained green even in winter, it was believed that mistletoe was a symbol of vitality and fertility.

However, it wasn’t until the 18th or 19th centuries that the plant began to make its way into our homes for holiday celebrations. One of the earliest mentions is an 1820 Washington Irving story that describes mistletoe being hung as a Christmas decoration.

2. It’s a parasite — sort of.

mistletoe in a treeWhile mistletoe doesn't always kill its host tree, it often reduces the tree's growth and can kill the branch where it resides. (Photo: bonchan/Shutterstock)

Mistletoe is a hemiparasitic plant because while it’s able to perform photosynthesis, the majority of nutrients it absorbs are from the tree or shrub where it has taken root — and that act can kill the host.

3. There’s mistletoe etiquette.

Some believe that after a man and woman kiss beneath the mistletoe, the man is supposed to remove one of the plant’s berries. Once the berries are all gone, there should be no more kissing beneath the mistletoe.

4. It’s about more than just kissing.

While sharing a kiss beneath the mistletoe is said to be good for your love life, not sharing one is said to bring bad luck to those who don't pucker up.

Another mistletoe custom involves young women placing a sprig beneath their pillows at night so they’ll dream about the man they’ll someday marry. In the morning, they’re supposed to burn the mistletoe, and if the flames burn steadily, they will have a happy marriage. (On the downside, a weak fire means the marriage will be an unhappy one.)

5. The origin of the name isn’t so kissable.

Some etymologists think the word roughly translates to “dung on a twig,” which makes sense considering how mistletoe’s seeds are spread.

When birds eat the plant’s berries, they don’t digest them, so when bird droppings fall on a tree or shrub, the seeds take root. Birds also help disperse the seeds by wiping their beaks on tree bark to clean off the seeds that stick after a meal. The berry’s sticky juice helps the steeds remain on the tree instead of falling to the ground.

bird eating mistletoeBirds can eat mistletoe, but it's toxic to many other animals, including dogs, cats and horses. (Photo: Utopia_88/Shutterstock)

6. Birds don’t just eat mistletoe, they often nest in it too.

A variety of bird species nest in mistletoe, including owls, doves, wrens and chickadees. In fact, researchers found that 64 percent of all Cooper’s hawk nests in northeastern Oregon were in mistletoe.

Also, because trees with mistletoe can die early from the parasitic growth, they become especially useful to nesting birds and mammals. A forest infested with mistletoe may produce three times more cavity-nesting birds than a forest without it, according to the National Wildlife Federation.

7. There are a variety of species.

There are 1,300 mistletoe species, and 20 of them are endangered. The continental U.S. and Canada are home to more than 30 species of mistletoe.

8. It’s toxic to pets.

While birds can eat mistletoe, the plant is poisonous to dogs and cats and can cause vomiting, diarrhea, seizures and even death. It’s not lethal to humans, but ingesting it can cause blurred vision, vomiting, a slowed heartbeat and even seizures. So, the next time you see it, steer clear of eating it and simply pucker up.