Kiss someone under the mistletoe and you're doing what the Druids did centuries ago. That's all that remains from the many mistletoe legends of European peoples of centuries ago.
A sprig of mistletoe wasn't always so innocent. Mistletoe was regarded by the ancients as having supernatural powers, sometimes good and sometimes evil. Two thousand years ago, mistletoe was known by some as a beneficial medicinal herb. In Scandinavian mythology, however, mistletoe was responsible for the destruction of the sun god Baldur the Beautiful.
Mistletoe is only a small wisp of a plant, so why would the ancients credit it with such awesome powers as healing or overpowering gods? The reason is because mistletoes are capable of killing large trees, even the massive oaks venerated by the Druids.
Mistletoes are parasitic plants. They nestle into the branches of host trees, then penetrate the bark to sap nutrients and water. This weakens and, in some cases, kills the tree. As the ancients gazed up into tree branches, they recognized that the tufts of mistletoe, though intimately associated with the tree, were nonetheless different from the rest of the tree. Our word "mistletoe" is a derivation of the Saxon word "mistl-tan," meaning "different twig."
European legends were based on their native mistletoe, known as true mistletoe. As the Americas were colonized, European customs were carried across the Atlantic and applied to one of the native mistletoes, called Christmas mistletoe or true American mistletoe. Christmas mistletoe is relatively rare, occurring in isolated pockets south of New Jersey, and then west to New Mexico. It lives on junipers and deciduous trees, but usually is not life-threatening to the host tree. In fact, Christmas mistletoe could be considered an agricultural crop, as it supports a Christmastime industry.
Not all native American mistletoes are innocuous. Another species, dwarf mistletoe, can devastate whole stands of forest trees.
Notice the white berries of mistletoe. Within the berries are sticky seeds, just right for sticking to the bark of a tree. Birds and other animals carry the seeds from tree to tree. In the case of dwarf mistletoe, the ripe seeds are shot out of the berries, often as far as 50 feet.
Where mistletoe is "cultivated," gardeners take the sticky seeds and sow them in the bark of a suitable host tree. Most gardeners prefer to get their mistletoe from the florist, using it as a plant for the doorway, not the garden.