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Mistletoe belongs to the family Viscaceae and to the genus Viscum, Phoradendron, or Arceuthobium. Most commonly, mistletoe refers to either the Eurasian shrub Viscum album or one of the American species, such as Phoradendron flavescens. Mistletoe grows on the trunks and branches of a wide variety of trees. Mistletoe is an evergreen, and its stems have numerous branches. The plants have tough, oblong, green leaves, tiny flowers, and waxy, translucent, white berries with a viscous mesocarp (the portion of the berry between the skin and seed).

Mistletoe in Florida. JLM Visuals. Reproduced by permission.

Mistletoe is considered to be a partial parasite or semi-parasite because it manufactures all of its carbohydrates through photosynthesis in its green leaves, but it depends on its host tree for water, minerals, and protein. There is one leafless flowering species of mistletoe of the genus Arceuthobium that is entirely parasitic and is damaging to conifers. A root-like structure (haustorium) of the mistletoe penetrates into the bark of the host tree and absorbs water, inorganic ions, sugars, amino acids, and hormones from the tree's xylem and phloem (inner and outer vascular parts of each stem). Dispersal of the seeds of these plants is primarily carried out by birds who eat the berries and fly to another tree, dropping the sticky berries onto the bark. Within days roots emerge from the germinating seed.

The tradition of kissing beneath the mistletoe is believed to come from a Norse legend in which Balder, the god of Peace, was killed with an arrow made of mistletoe. As the story goes, the gods bring Balder back to life by giving mistletoe to Freya, the goddess of Love, who makes the plant a symbol of love. Freya proclaimed that anyone who passed under mistletoe could be kissed. The Druids used mistletoe to welcome the new year and for religious rites and medicinal purposes, such as treating sterility and epilepsy. The French name for mistletoe, herbe de la croix (herb of the cross), comes from a legend describing how mistletoe was once a tree that was used to make Christ's cross. According to legend, after Christ's death, mistletoe was cursed to never again grow from the earth and it was turned into a small parasite. Mistletoe was also associated with magical powers in some cultures, and is thought to have been the Golden Bough that opened the door to the Underworld for Sybil and for the hero Aeneas in Virgil's Aenead.

Each species of mistletoe has unique chemical properties and different medicinal possibilities. Hundreds of years ago mistletoe was used for a variety of ailments and conditions. Currently, the potential medicinal effects of mistletoe are being tested on laboratory animals. Some research is being done to see if certain extracts from mistletoe can destroy cancer cells. Along with some potentially beneficial substances, mistletoe contains toxic substances and therefore should not be eaten.

Christine Miner Minderovic

Additional topics

Science EncyclopediaScience & Philosophy: Methane to Molecular clock