What we commonly call the Mistletoe actually belongs to a species of parasitic plants that live off the water and nutrients of a host plant which can be any tree or bush. The Mistletoe plant propagates itself through the wanderings of birds who eat the berries of the plant and then spread the undigested seeds through their excrement, by regurgitation, or by wiping the seeds stuck to their bills on an appropriate branch. The seeds are coated with a sticky material that allows them to cling to the limbs of branches where they take root.
It may not be the holiday story you were hoping for, but the truth is Mistletoe plays an important role in nature by providing biodiversity.
While no part of the plant is edible for humans, a number of other animals rely on it for food and shelter. Areas with greater mistletoe densities support higher diversification of plants and animals. This is what fuels the association of mistletoe with fertility and vitality. This is no doubt behind the longstanding tradition for lovers to kiss while standing under the mistletoe.