Mistletoe, while being a happy symbol during the Christmas season requiring a kiss if found standing under it, is in reality a parasite which can kill trees that become heavily infested, as is this Oak tree. From the earliest times mistletoe has been one of the most magical, mysterious, and sacred plants of European folklore. It was considered a bestower of life and fertility; a protectant against poison; and an aphrodisiac. The mistletoe of the sacred oak was especially sacred to the ancient Celtic Druids. Mistletoe was long regarded as both a sexual symbol and the "soul" of the oak. It was gathered at both mid-summer and winter solstices, and the custom of using mistletoe to decorate houses at Christmas is a survival of the Druid and other pre-Christian traditions.