Why do people hang up mistletoes every Christmas in the hopes of getting a kiss from their loved ones? The history of this tradition is actually quite interesting.

Botanist Carlos Reif shared in a TED-Ed video that the custom surrounding the "kissing plant" can be attributed to European folklore and mythology.

"The long-lived custom intertwines the mythology and biology of this intriguing plant. There are more than 1,000 species of mistletoe which grows the world over. In fact, the ancient Europeans were so captivated by the plant's unusual growth habits that they included it in their legends and myths," he shared.

One Scandinavian legend told of the god Baldr and his adoring mother Frigg, goddess of love, marriage and fertility. She was so enamored with her son that she ordered every plant, animal and inanimate object never to harm him — but she forgot about the mistletoe.

The mischievous god Loki decided to take advantage of this by piercing Baldr's heart with an arrow carved from a mistletoe's branch. Frigg was so heartbroken over what happened that fellow gods decided to resurrect Baldr.

She was so grateful by what they did that she decided to turn the mistletoe from a symbol of death into one of peace and love. Now, whenever people passed by the plant, they are mandated to kiss and hug to spread more love into the world.

"But this custom comes down to more than just human imagination," said Reif. "All of it was inspired by the plant's intriguing biology. We see mistletoe as a festive decoration, but draped on tree boughs in the wild, it's known as a partly parasitic plant. Mistletoe relies on modified roots called haustoria that penetrate the tree bark and siphon off the minerals and water trees carry up their trunks."

The only way the plant can colonise nearby trees is with its seed, which are dispersed by birds and other creatures. Birds that eat the mistletoe's sticky white berries try to get rid of the gluey seeds by wiping them off onto the tree bark, and sometimes, they excrete the indigestible seed onto a tree where it germinates and start to grow.

"With its resilience and foliage that stays lush even while the surrounding trees lose their leaves, mistletoe fascinated our ancestors," Reif explained. "They saw this as signs of the plant's magical qualities and fertility."