Mistletoe is a parasitic shrub-like plant found growing on hardwoods, especially in swamps. These evergreen plants are more readily seen during the winter when the leaves are off their "host" trees. The presence of these green clusters on the otherwise bare trees, led the Druids to believe that mistletoe represented the spirit of its host plant and had mystical qualities. The hanging of mitletoe over doorways at Christmas time originated from early Druid practices.