The Secret Life of Mistletoe
Author: Kelsey Laymon, Research Scientist
The trees are starting change color and drop their leaves and you might be asking yourself, “What is that ball of green still left?” That ball of green is actually Mistletoe. Long before mistletoe became an excuse to steal a kiss, it became a widespread and important species in ecology. Mistletoe is a diverse group of flowering plants with over 1,300 species that reside in habitats all across the world. They use a unique growth form called obligate hemiparasitism, meaning they attach to a host through a vascularized root called a haustorium to obtain water and nutrients. They perform about 40% of their own photosynthesis, which is why they are only hemiparasitic and not fully parasitic. They can infect a wide variety of hosts including coniferous trees, cacti, succulents, orchids, ferns and even grasses.
The mistletoe’s seeds are deposited with a sticky material that helps adhere onto a branch of a tree or shrub. The seed germinates and produces a hypocotyl, or stem of a seedling, which grows towards the bark of the host depending on gravity and light. After about a full year, the hypocotyl penetrates the bark to reach the conductive tissues of its host. Often when mistletoe attaches to its host tree, they will stunt the growth of the tree and a heavy infestation can actually kill the tree. However, mistletoe fruits are high in soluble carbohydrates, minerals and amino acids and therefore are an excellent food source for birds and mammals. Because the fruits are available year round, 66 families of birds and 30 families of mammals have been recorded as eating mistletoe fruit. Furthermore, mistletoe flowers provide nectar that many insects and mammals consume.
In addition to providing food sources to a number of species, mistletoe is used for nesting and roosting sites for over 43 families of birds and 7 families of mammals. The Long-eared Owl uses mistletoe clumps as a structural foundation for their stick nests. Other birds use mistletoe to help conceal their nests from predators. In addition, mistletoe clumps are used as a hiding place from predators, and a shelter from hot temperatures. Interestingly it has been documented that fresh mistletoe sprigs are used as nest linings and can play a key role in the hygiene of the nests because the sprigs have antibacterial properties.
David M. Watson suggested that mistletoe functions as a keystone species, or a species that has a large effect on its environment relative to its abundance. Through two case studies, one a semiarid shrub habitat and the other a temperate forest, Watson found that mistletoe has a large impact on the biomass, species abundance, nutrient resources and nesting sites in these environments. Watson suggests due to his findings that mistletoe should be considered a keystone resource. Although mistletoe is a hemiparasitic plant and could be deadly to a tree, it actually helps to enhance the surrounding environment in most cases. Many animals use mistletoe for its unique properties and can be useful for its antibacterial properties. Mistletoe
For The American Heritage® Medical Dictionary:
immunostimulant. (n.d.) The American Heritage® Medical Dictionary. (2007). Retrieved December 18 2014 from http://medical-dictionary.thefreedictionary.com/immunostimulant
“haustorium”. Encyclopædia Britannica. Encyclopædia Britannica Online.
Encyclopædia Britannica Inc., 2014. Web. 18 Dec. 2014
“Keystone Species.” National Geographic. Web. 18 Dec. 2014. <http://education.nationalgeographic.com/education/encyclopedia/keystone-species/?ar_a=1>.
Tainter, Frank H. “What Does Mistletoe Have To Do With Christmas?” APS. Clemson University. Web. 18 Dec. 2014. https://www.apsnet.org/publications/apsnetfeatures/Pages/Mistletoe.aspx
Watson, David M. “Mistletoe-A Keystone Resource in Forests and Woodlands Worldwide.” Annu. Rev. Ecol. Syst. 2001 (2001): 219-47. Print.