Like poinsettia, holly, pine, and fir trees, mistletoe is also associated with the winter holiday season. Partially-parasitic plants in the genera Viscum, Arceuthobium, and Phoradendron are all called mistletoe. Host species infested with mistletoe often have abnormal growth and are susceptible to wood-boring insects, fungi, and other pathogens. Heavy infestations of mistletoe can also cause limb death on host trees.
Viscum album (European mistletoe) is native to Europe, often found growing in poplar, apple, and hawthorn trees. It was introduced into California by Luther Burbank in the early 1900's and is now found on 23 deciduous tree species, including apple, pear, poplar, silver maple, black locust, and red alder. European mistletoe plants have pale green leaves that turn yellow when dried. Leafy mistletoes, including V. album and Phoradendron species, are not found in cold regions since they are susceptible to sub-freezing temperatures.
There are about 42 species of Arceuthobium, known as dwarf mistletoes that infect conifers. In the western United States, dwarf mistletoes cause an estimated loss of 3.3 billion board feet of wood annually. These mistletoes have scale-like leaves and dioecious flowers (male and female flowers on separate plants).
American mistletoe (Phoradendron leucarpum), commonly sold during the holiday season, is generally harvested from trees growing in Oklahoma and Texas. American mistletoeis found in 16 counties in Missouri, mostly in the southeastern area of the state. Like European mistletoe, P. leucarpum is an evergreen shrub that parasitizes several types of deciduous trees growing in bottomland forests and along streams and rivers. Host trees for American mistletoe include river birch, blackgum, swamp tupelo, American elm, etc. However, sycamore (Platanus occidentalis) is the most common host for mistletoe in Missouri.
American mistletoe is visible as a dense mass of green vegetation called "witches' brooms", growing in deciduous trees after leaf fall. American mistletoe is considered hemiparasitic or semi-parasitic because it obtains water and mineral nutrients from the host tree, but it also derives nutrition from photosynthesis. In Greek, the scientific name for American mistletoe, Phoradendron, means "thief of the tree." Aristotle (384-322) believed that mistletoe was spontaneously generated, but his pupil, Theophrastus (371-287 BC) wrote that mistletoe grew from seed deposited in bird feces. Anglo-Saxons also knew the origin of these plants as the Old English translation of mistletoe is "twig dung". Sticky mistletoe seeds germinate and produce a specialized structure, known as a haustorium. These structures grow through the bark and into the xylem of the host tree to absorb water and nutrients. Eventually, mistletoe shoot growth occurs, forming a shrub on the host plant, without aerial roots. Inconspicuous flowers bloom in late fall and the white sticky berries, borne in small clusters, mature a year later.
European mistletoe is associated with several legendary tales. Greek philosopher, Pliny the Elder (23 to 79 BC) wrote that mistletoe cut from oak trees had mystical healing powers as long as it didn't touch the ground when harvested. In Virgil's (29 to 19 BC) epic poem, "Aeneid", two doves guide the Trojan hero, Aeneas, through a forest to a tree where he discovers mistletoe (i.e., the "golden bough"). After showing the bough to a ferryman, Aeneas is allowed to cross the Stygian river and enter the netherworld. In sacred rituals, Druids cut mistletoe from an oak tree with a golden sickle for a special drink to increase fecundity in barren animals. In Norse mythology, Frigga, the goddess of love and marriage has a son named Baldur who is accidently slain by his blind brother, using an arrow made from mistletoe wood. Afterwards, Frigga's tears turn into mistletoe berries and Baldur comes back to life. During the Middle Ages, mistletoe was hung from ceilings or above doors to ward off evil spirits and ensure fertility. In Sweden, European mistletoe was kept in homes to prevent fire.
Kissing under a sprig of mistletoe dates back to the 16th century. A poem written in 1826 refers to plucking a berry from the mistletoe after each kiss beneath the bough. In illustrated 19th century versions of Charles Dicken's "The Pickwick Papers", young maidens surround portly Samuel Pickwick for a kiss. Also in some parts of England, mistletoe burned on the twelfth night ensured marriage for those who kiss beneath it. Yet another custom is that couples should kiss under the mistletoe to ensure good luck.
Perhaps one of the earliest accounts of using mistletoe for medicinal purposes was written by Pliny (23 to 79 BC). For the treatment of epilepsy, a mistletoe decoction was administered or the patient carried a sprig of mistletoe with them. Since mistletoe was attached to tree limbs, it couldn't fall to the ground. Thus, it was reasoned that an epileptic carrying mistletoe or had swallowed the decoction, also wouldn't fall to the ground. Interestingly, mistletoe was used to treat this disease up to 1900 AD.
Native Americans used P. leucarpum to treat toothaches, measles, cholera, convulsions, hysteria, nervous disorders, and heart problems. However, mistletoe is considered a poisonous plant when ingested. American mistletoe stems, leaves, and berries contain phoratoxin, which can cause blurred vision, nausea, abdominal pain, diarrhea, etc. European plants contain viscotoxin, which tends to be more toxic than American mistletoe. Thus, artificial sprigs of mistletoe are a safe alternative to the live plant, especially around children or pets.
Although mistletoe may be considered a noxious plant by some, it is useful for many animal and insect species. Birds, including grouse, mourning doves, bluebirds, evening grosbeaks, robins and pigeons feed on mistletoe. Others, such as silky flycatchers, several types of owls, red crossbills, house wrens, pygmy nuthatches, chickadees, chipping sparrows, Cassin's finches, pine siskins, etc., use the witches' brooms of mistletoe for nesting sites. Butterflies, including the great purple hairstreak, feed on American mistletoe and the thicket hairstreak and the Johnson's hairstreak feed on dwarf mistletoes. For honeybees and other native bees, nectar and pollen from mistletoe flowers are a food source. Twig beetles, some thrips, a plant bug species, elk, deer, cattle, squirrels, chipmunks, and porcupines also feed on mistletoe. Thus, mistletoe has its place in nature and in our homes as a festive holiday symbol.
REVISED: February 21, 2017