To this day, mistletoe—a parasitic plant that grows on oak and other non evergreen trees—is the only form of greenery not allowed inside many Christian churches during the holiday season. That’s because although other greenery was also used in pagan festivals, mistletoe was actually worshiped.
Both Druids and Romans considered the plant sacred, as a healing plant and a charm against evil. Mistletoe was thought to be the connection between earth and the heavens, because it grew without roots, as if by magic. It was also considered a symbol of peace; warring soldiers who found themselves under mistletoe quickly put down their weapons and made a temporary truce. In a related custom, ancient Britons hung mistletoe in their doorways to keep evil away. Those who entered the house safely were given a welcome kiss.
While the custom of kissing under the mistletoe lost popularity in most other countries, it remained popular in England and the United States. Today, most consider mistletoe an excuse for kissing and nothing more, but some people in France still brew it as a cure for stomach aches.