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What is mistletoe?

As I reflect back on Christmases past, I remember my mother hanging up mistletoe in a hallway arch between the living room and dining room. Also, I am sure that you have heard the lyrics to that wonderful old holiday song, “I Saw Mommy Kissing Santa Claus.”But what is mistletoe really and how did the customs associated with it arise?

Mistletoe is an evergreen parasitic plant, and grows on the branches of trees, where it forms pendent bushes 2-5 feet in diameter. It will grow and has been found on almost any deciduous tree, preferring those with soft bark.

When one of the sticky berries of the mistletoe comes into contact with the bark of a tree — generally through the assistance of birds — after a few days it sends forth a thread-like root, flattened at the extremity like the proboscis of a fly. The root pierces the bark and then anchors itself firmly in the growing wood. It can then select for its own use, such juices as are fitted for its survival. It is interesting that the wood of mistletoe has been found to contain two times as much potash and five times as much phosphoric acid as the wood of the tree to which it is attached. Mistletoe is a true parasite, for at no period of its existence does it derive nourishment from the soil, or from decayed bark, like some of the fungi do. All its nourishment is obtained from its host.

The stem is yellowish and smooth, freely forked, separating when dead into bone-like joints. The leaves are tongue-shaped, broader toward the end, 1-3 inches long. They’re very thick and leathery, of a dull yellow-green color, arranged in pairs, with very short footstalks. The flowers — small and inconspicuous — are arranged in threes, in close short spikes or clusters in the forks of the branches. They are of two varieties, the male and female occurring on different plants. Neither male nor female flowers have a corolla, the parts of the fructification springing from the yellowish calyx. They open in May. The fruit is a globular, smooth, white berry, ripening in December.

The English name is said to be derived from the Anglo-Saxon Misteltan, “tan” signifying twig, and “mistel” from “mist.” The Latin name of the genus, Viscum, signifying sticky, was assigned to it from the glutinous juice of its berries.

The ancient Druids held mistletoe in great reverence. They believed the mistletoe protected its possessor from all evil, and that the oaks on which it was seen growing were to be respected because of the wonderful cures that the priests were able to effect with it. They sent round their attendant youth with branches of the mistletoe to announce the arrival of the new year. It is probable that the custom of including it in the decoration of our homes at Christmas and giving it a special place of honor is a result of this old custom. If you hang up some mistletoe, I challenge you to see if you can catch Santa under it this Christmas.

Bill Lamont is a professor emeritus in the department of plant science at Penn State and can be reached by email at wlamont@psu.edu.