Mistletoe traditionally gets lots of attention this time of year in holiday carols and decorations. This group of plants has interesting and unique characteristics and is associated with both traditions and myths that go back to ancient times.

Mistletoes make up a large group of plants that are all parasitic, which is probably where many myths originate from. Rather than rooting into soil, their roots enter host trees or shrubs and then obtain water and nutrients from the host plant. As a result, new plants may suddenly appear growing up in a tree, leading to all sorts of speculation in ancient times as to why and how; perhaps some power was involved. Bird droppings were also believed to sprout into mistletoe. Hence the various mysterious beliefs and myths associated with mistletoe.

Today we know mistletoe may be grouped as either full or partial parasites. Mistletoes associated with holiday decorations are in the group classified as partial parasites. As like other plants, they still produce their own food (energy) through photosynthesis, in addition to obtaining some nutrients from their host plant. That host tree is rooted in soil.

The host tree continues to live and despite the parasite is not seriously deprived of nutrients, but the amount of rooting parasitic plants, or infections, is important. Just a few and the tree is stunted but overall looks healthy. Numerous penetrating roots may cause trees to be stressed to the point where secondary problems, such as insects or disease, may become serious issues for the tree.

The mistletoe typically associated with Christmas decorations is native to about the Eastern one-third of the United States and is the state flower of Oklahoma. More than one hundred species of deciduous trees are potential hosts, most notably American Elm. All parts of the plant are toxic if ingested in copious quantities, in particular the white berries that develop in summer.

Although not associated with holiday decorations, dwarf mistletoes fall into another classification group considered full parasites. They will parasitize conifers, with each dwarf mistletoe species usually infesting a single conifer species. Oftentimes witches’ brooms, or tight clusters of deformed twig growth, develop as the result of roots penetrating host tree branches. Growth rate of trees will be reduced.

These types of mistletoe are leafless and will eventually kill the host tree. In the western United States dwarf mistletoe is a serious pathogen in conifers in the forestry industry, leading to significant economic losses. Not only can they kill trees directly as parasites, but stressed trees also become very prone to bark beetle infestations. Bark beetles will infest stressed trees and kill them off.