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Kissing under mistletoe is a holiday tradition. How did it become one?

Recently, I had the opportunity to share some holiday cheer with Deanna Behring and her office staff in the College of Agriculture. One of the holiday songs that I sang was “I Saw Mommy Kissing Santa Claus” and it brought back memories of my mother hanging up mistletoe in a hallway arch between our living room and dining room. The office staff wanted to know more about mistletoe — what it it, really, and how did the customs associated with it arise?

Mistletoe is an evergreen parasitic plant, growing on the branches of trees, where it forms pendent bushes, 2 to 5 feet in diameter. It will grow and has been found on almost any deciduous tree, although preferring those with soft bark. I have seen it on oak trees when hunting.

When one of the sticky berries of the mistletoe comes into contact with the bark of a tree assisted by the activities of birds it will after a few days send 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. Mistletoe is a true parasite, for at no time during 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 to 3 inches long. They tend to be very thick and leathery with a dull yellow-green color, arranged in pairs, with very short footstalks. The flowers are small and inconspicuous and arranged in threes, in close short spikes or clusters in the forks of the branches. Neither male nor female flowers have a corolla, the parts of the fructification springing from the yellowish calyx. The flowers open in May and 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. The Druids held that 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 which 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. It was also used as a sign of love and friendship in Norse mythology and that’s where the custom of kissing under mistletoe seems to have originated.

I challenge you to see if you can catch Mommy kissing Santa under the mistletoe this Christmas.

Bill Lamont is professor emeritus in the department of plant science at Penn State and can be reached by email at