Mistletoe and Holly
Two hundred years before the birth of Christ, the Druids used mistletoe to celebrate the coming of winter. They would gather this evergreen plant that is parasitic upon other trees and used it to decorate their homes. They believed the plant had special healing powers for everything from female infertility to poison ingestion. Scandinavians also thought of mistletoe as a plant of peace and harmony. They associated mistletoe with their goddess of love, Frigga.  According to a Christmas custom, any two people who meet under a hanging of mistletoe are obliged to kiss. The custom was described by Washington Irving in his 1820  ”The Sketch Book of Geoffrey Crayon”:

The mistletoe is still hung up in farm-houses and kitchens at Christmas, and the young men have the privilege of kissing the girls under it, plucking each time a berry from the bush. When the berries are all plucked the privilege ceases.

The early church banned the use of mistletoe in Christmas celebrations because of its pagan origins. Instead, church fathers suggested the use of holly as an appropriate substitute for Christmas greenery.

From the Symbols and Traditions of Christmas and Christmas Eve and from Washington Irving, The Sketch-Book Of Geoffrey Crayon, Gent.” (Rev. Ed. 1852), p.254.