Mistletoe: a Kiss of Death?

Many plants help usher in the good cheer of the holiday season—Christmas trees, holly, poinsettias. But one plant, mistletoe, is not as harmless as it appears. Although people view mistletoe as a symbol of romance and peace, to a tree, mistletoe is a serious threat.

Mistletoe is a parasitic plant, which means that it gets its water and/or nutrients from another living organism. Most mistletoes have green leaves and stems and are able to make food with the power of sunlight, but they do not have roots to take up water and mineral nutrients. Instead, mistletoes have root-like projections called haustoria. Rather than living in the soil, the haustoria penetrate the water-conducting tissues of a living tree, and then the mistletoe is able to steal water and minerals from the host tree. Because of this, mistletoe is sometimes called "vampire plant".

Mistletoe can grow on hundreds of kinds of trees, both deciduous and evergreen. An infected tree may be significantly weakened, and may even die if many mistletoes infect it simultaneously. During dry conditions, most trees adjust so that they use less water; but mistletoes make no such adjustments, so they are especially stressful to trees during droughts. Luckily, only one species of mistletoe grows in Iowa, and only in the southern counties, on walnut trees. Many more species of mistletoe live in the southern US, where it is a serious problem for foresters.

There are about 1500 species of mistletoe worldwide, but the one we usually buy for a holiday decoration is Phoradendron flavescens, a leafy mistletoe with waxy, white berries. Because those berries are poisonous, they are often replaced with fake berries before sale. Most holiday mistletoe is harvested in Oklahoma and Texas, where it are naturally abundant on a variety of trees.

The next time you steal a kiss under the mistletoe remember that the harmless-looking plant is not as friendly as it may appear.

Mistletoe hanging in the doorway at the ISU Plant and Insect Diagnostic Clinic

Mistletoe hanging in the doorway at the ISU Plant and Insect Diagnostic Clinic


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