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Mistletoe. A Special Lesson Produced by: Joan Jackson & Dr. Frank B. Flanders Georgia Agricultural Education Curriculum Office April 2002 Teachers should view notes pages for additional information on certain slides. View note pages by clicking on ‘View’ and then ‘Notes Page’.

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A Special Lesson

Produced by: Joan Jackson & Dr. Frank B. Flanders

Georgia Agricultural Education Curriculum Office

April 2002

Teachers should view notes pages for additional information on certain slides.

View note pages by clicking on ‘View’ and then ‘Notes Page’

Click HERE for more information about the authors.

introduction to mistletoe
Introduction to Mistletoe
  • Mistletoe is one of our best-known, but least understood plants. Although, familiar to everyone at Christmas, with a history in folklore and legend, little is known about this strange plant other than kissing under the mistletoe as a Christmas tradition.
mistletoe is a vampire
Mistletoe is a Vampire
  • It survives by sucking nutrients from the host tree, sometimes killing the tree although mistletoe has a vested interest in keeping the tree alive. For this reason, mistletoe is sometimes known as “the vampire plant.”
mistletoe is a freeloader
Mistletoe is a Freeloader
  • It is parasitic on the stems of woody plants, from which it derives water, mineral nutrients, and organic compounds carried in xylem sap.
mistletoe is a thief
Mistletoe is a Thief
  • It’s scientific name, Phoradendron, means “thief of the tree” in Greek. The mistletoe plant puts its roots down into tree limbs in order to steal water and nutrients.

Mistletoe is semi parasitic; that is, it has green leaves that provide some energy meets many of its energy by sucking the life blood from its host, usually oaks, elms, and poplars.

what is mistletoe
What is Mistletoe?
  • The well-known Mistletoe is an evergreen parasitic plant, growing on the branches of trees, where it forms pendent bushes, 2 to 5 feet in diameter.
what is mistletoe cont
What is Mistletoe cont.
  • Evergreen clumps of mistletoe are readily observed on deciduous trees in winter when leaves are off the trees.
what is mistletoe cont8
What is Mistletoe cont.
  • Mistletoe is especially interesting botanically because it is a partial parasite (a “hemi parasite”). As a parasitic plant, it grows on the branches or trunk of a tree and

actually sends out roots that penetrate into the tree to take up nutrients. But mistletoe is also capable of producing its own nutrients by photosynthesis.

what is mistletoe cont9
What is Mistletoe cont.
  • American mistletoe (Phoradendron species) can be found growing in deciduous trees from New Jersey and southern Indiana southward to Florida and Texas. It is also the state flower of Oklahoma.
what is mistletoe cont10
What is Mistletoe cont.
  • Most of the mistletoe sold during the holiday season is gathered in the wild. Most mistletoe is harvested in Oklahoma and Texas.
how did mistletoe get its name
How did Mistletoe get its Name?
  • The common name of mistletoe is derived from the ancient belief that mistletoe was propagated from bird droppings. This belief was related to the then-accepted principle that life could spring spontaneously from dung.
how did mistletoe get its name cont
How did Mistletoe get its Name? cont.
  • It was observed in ancient times that mistletoe would often appear on a branch or twig where birds had left droppings. “Mistel” is the Anglo-Saxon word for “dung,” and “toe” is the word for twig. So, mistletoe means “dung-on-a-twig.”
the sex of mistletoe
The Sex of Mistletoe
  • Mistletoe plants are either male (produce only pollen) or female (produce berries).
the sex of mistletoe cont
The Sex of Mistletoe cont.
  • All species of mistletoe in the United States are dioecious meaning they have male and female flowers on separate plants. Male plants produce only pollen, and female plants produce flowers and fleshy, white seed pods. Each pod is filled with a slimy and sticky clear fluid and one seed covered with a tough greenish membrane (see photos below).
why is mistletoe green if it is parasitic
Why is mistletoe green if it is parasitic?
  • Technically speaking, mistletoe is a semi-parasite, although it steals water and nutrients from a host plant. It has green leaves from chloroplasts used in photosynthesis.
  • Mistletoe plants develop well in full sunlight and reach most extensive development high in the crowns of large trees where it can obtain the light needed for photosynthesis.
legends and traditions
Legends and Traditions
  • The traditions, which began with the European mistletoe in ancient times, were transferred to the similar American plant with the process of immigration and settlement.
legends and traditions cont
Legends and Traditions cont.
  • In the Middle Ages and later, branches of mistletoe were hung from ceilings to ward off evil spirits. In Europe they were placed over house and stable doors to prevent the entrance of witches.
legends and traditions cont18
Legends and Traditions cont.
  • In Scandinavia, mistletoe was considered a plant of peace, under which enemies could declare a truce or disagreeing spouses could kiss and make-up.
legends and traditions cont19
Legends and Traditions cont.
  • In some parts of England the Christmas mistletoe is burned on the twelfth night lest all the boys and girls who have kissed under it never marry.
legends and traditions cont20
Legends and Traditions cont.
  • Kissing under the mistletoe is first found associated with the Greek festival of Saturnalia and later with primitive marriage rites. Mistletoe was believed to have the

power of bestowing fertility, and the dung from which the mistletoe was thought to arise was also said to have “life-giving” power.

legends and traditions cont21
Legends and Traditions cont.
  • And for those who wish to observe the correct etiquette: a man should pluck a berry when he kisses a woman under the mistletoe, and when the last berry is gone, there should be no more kissing!
legends and traditions cont22
Legends and Traditions cont.
  • In the first century, the Druids in Britain believed that mistletoe could perform miracles, which ranged from providing fertility to humans and animals to healing diseases and protecting people from witchcraft.
legends and traditions cont23
Legends and Traditions cont.
  • The Druids believed mistletoe could influence human fertility and was prescribed to individuals who had problems bearing children. Mistletoe has also been used in medicine as treatment of pleurisy, gout, epilepsy, rabies, and poisoning.
traditions of mistletoe cont
Traditions of Mistletoe cont.
  • Plastic mistletoe has become a fairly common substitute in recent years because real mistletoe has poisonous berries.  It's all part of the fun of Christmas, but some consider it a shame to devalue traditions by using fake material.
traditions of mistletoe cont25
Traditions of Mistletoe cont.
  • Because of its association with pagan ceremonies, mistletoe was banned from Christmas ceremonies by the Church in Medieval times.
traditions of mistletoe cont26
Traditions of Mistletoe cont.
  • A common medieval belief held that mistletoe was the wood used to make the crucifix.Cursed, mistletoe was no longer welcome on earth and was doomed to live as a parasite growing on trees. It was not until the 17th century that people became more open about their fondness for mistletoe.
what genus species is mistletoe
What Genus/Species is Mistletoe?
  • The mistletoe that is commonly used as a Christmas decoration, genus Phoradendron flavescens, is native to North America.
what genus species is mistletoe cont
What Genus/Species is Mistletoe? cont.
  • Phoradendron (American mistletoes)
  • There are some 1500 species of mistletoes worldwide.
  • Phoradendron is a large genus (perhaps 170 species) of primarily tropical and subtropical evergreen plants restricted to the Americas. Twelve species occur in the United States.
seed dispersal
Seed Dispersal
  • The small, sticky, whitish berries are produced from October to December. American mistletoes are most often distributed by birds. Birds avoid the immature fruits which are bitter, hard and contain poisonous compounds.

Instead, they eat mature fruits, however, they are still hard to digest.

seed dispersal cont
Seed Dispersal cont.
  • The birds ingest the fruit and digest the pulp, but the seeds quickly pass through the intestinal tract, retaining a sticky covering of hair-like threads that serve as glue to adhere them to the surface on which the remaining seeds fall.
seed dispersal cont31
Seed Dispersal cont.
  • Another way birds spread seeds is when the birds clean their bills by rubbing them against the branches or bark of trees because the sticky seeds of mistletoe tend to cling to the bills of birds.
seed dispersal cont32
Seed Dispersalcont.
  • In most cases, the initial infestation occurs of mistletoe on larger or older trees because birds prefer to perch in the tops of tall trees.
seed dispersal cont33
Seed Dispersal cont.
  • While broadleaf mistletoe seeds are dispersed by birds, dwarf mistletoe seeds are spread mostly by their random forcible discharge from fruit, which can propel seeds horizontally into trees up to 30 to 40 feet away.
seed dispersal cont34
Seed Dispersal cont.
  • Seeds are capable of germinating anywhere if temperature and moisture are suitable, but only seeds that lodge on thin bark of twigs and small branches of a suitable host will cause infection.
seed dispersal cont35
Seed Dispersal cont.
  • A heavy buildup of mistletoe often occurs within an infested tree because birds are attracted to the berries, and may spend a significant amount of time feeding on them and depositing their droppings.

In addition, seeds may fall from mistletoe plants in the upper part of the tree, creating new infestations on the lower branches.

  • Seeds are rapidly defecated by birds while they still have their slimy, sticky coating. This allows the seeds to cling to a branch, sprout and insert its root-like "haustoria" into the water-conducting system of the tree.
germination cont
Germination cont.
  • Upon germination, the radical flattens itself against the bark, forming an attachment disc or holdfast. A multicellular projection called the

primary haustorium grows from the undersurface of the holdfast and penetrates the bark, often through lenticels or auxiliary buds.

germination cont38
Germination cont.
  • It takes many years for mistletoe to grow large enough to produce flowers and seeds. The haustoria in mistletoe both penetrates the water-conducting tissue of the trees (water transport) and infiltrate in between the cells where they absorb most nutrients.
germination cont39
Germination cont.
  • Once beneath the periderm in living cortical tissue or secondary phloem, the primary haustorium produces a radiating system of branches termed cortical strands or cortical haustoria. Wedge-shaped projections called sinkers grow from the cortical strands and pass through the cambium to the outer surface of the lignified xylem.
germination cont40
Germination cont.
  • Certain cells within the sinker differentiate into water-conducting tracheids and vessels. Some of these come into intimate contact with vessels or tracheids of the host such that open pits and perforations connect the water-conducting systems of the two plants. This assures transport of water and minerals to the parasite.
germination cont41
Germination cont.
  • Activity of this meristem is synchronized with that of the host so that the sinker elongates as the host stem increases in radius.Aerial shoots begin to grow after the

system of cortical stands and sinkers is initiated. The first shoots arise from buds on the holdfast, and they grow only a few millimeters during the first year.

is mistletoe poisonous
Is Mistletoe Poisonous?
  • Some mistletoes are poisonous to humans, especially some of the true or leafy mistletoes of hardwood trees, but it typically takes ingestion of numerous leaves or shoots of a mistletoe plant to affect an adult. Children and pets on the other hand, are much smaller and are affected by much less of a plant.
is mistletoe poisonous cont
Is Mistletoe Poisonous? cont.
  • Although mistletoe has been used in the treatment of several ailments, the berries are poisonous. Individuals using mistletoe during the holiday season should keep the sprigs out of the reach of

children. For safety reasons, many companies have replaced the berries with artificial, plastic berries.

how does mistletoe invade a tree
How does Mistletoe invade a tree?
  • After arriving on a host, a typical mistletoe seed's first exploratory root grows away from light, and into the crevices of the bark of a limb or tree trunk.

Once inside the bark, the mistletoe sends in special wedge tissue in search of the plumbing.

how does mistletoe invade a tree cont
How does Mistletoe invade a tree? cont.
  • Hitting the host's network of water-carrying cells deep inside the plant, the mistletoe builds its own system of ducts to steal water and nutrients. After the mistletoe seed germinates, it grows through the bark and into the tree's water-conducting tissues, where root-like structures called haustoria develop.
how does mistletoe invade a tree cont46
How does Mistletoe invade a tree? cont.
  • The haustoria gradually extends up and down within the branch as the mistletoe grows. Initially, the parasitic plant grows slowly;

it may take years before the plant blooms and produces seeds. Broadleaf mistletoes have succulent stems that become woody at the base.

how does mistletoe invade a tree cont47
How does Mistletoe invade a tree? cont.
  • Initial infection usually occurs on a small branch and is followed by multiple infections on the same tree after the initial plant produces fruit.

The dominant symptom caused by mistletoe is atrophy (meaning wither) and dieback of branch ends beyond the point of attachment of the parasite.

how does mistletoe invade a tree cont48
How does Mistletoe invade a tree? cont.
  • Mistletoe may increase dramatically within a single tree where birds roost, feed on berries, and deposit seeds on twigs and branches. Multiple infections result in loss of vigor, dieback, and often death (to the tree).
how does mistletoe invade a tree cont49
How does Mistletoe invade a tree? cont.
  • Bark tissues of host and parasite meet in a convoluted line at the swollen union. Dissection shows continuity of xylem of host and parasite.
how does mistletoe invade a tree cont50
How does Mistletoe invade a tree? cont.
  • Mistletoe has developed a very specialized tissue with the shape of a bell (called a haustorium). This bell-shaped structure grows into the host tree and combines with the living tree.
does mistletoe hurt trees cont
Does Mistletoe hurt trees? cont.
  • Broadleaf mistletoe absorbs both water and mineral nutrients from its host trees. Healthy trees can tolerate a few mistletoe branch infections, but individual branches may be weakened or sometimes

killed. Heavily infested trees may be reduced in vigor, stunted, or even killed, especially if they are stressed by other problems such as drought or disease.

does mistletoe hurt trees cont52
Does Mistletoe hurt trees? cont.
  • People passing through a forest may dismiss mistletoes as relatively harmless since these parasites do not seem to do much damage. But over the tree’s life span, damage can be significant, but not noticed by humans for years to come.
does mistletoe hurt trees cont53
Does Mistletoe hurt trees? cont.
  • Economic damage by Phoradendron species of mistletoe is considered to be slight, although other species of mistletoe cause much more sever damage. The damage caused by mistletoe in Georgia is best described as tree decline.
how does mistletoe damage trees
How does Mistletoe damage trees?
  • Mistletoe tissues are capable of maintaining greater osmotic potential than tissues of the host; thus the parasite preferentially receives water during times of water shortage. In simpler terms,

mistletoe really sucks – its pull of water through the trees xylem is stronger than that of the tree and it will obtain water when the tree is thirsting to death.

how does mistletoe damage trees cont
How does Mistletoe damage trees? cont.
  • Mistletoes also waste water by continuing to transpire even when under water stress. This causes abnormally

severe water stress in hosts and is considered to contribute to dieback and loss of vigor.

how does mistletoe damage trees cont56
How does Mistletoe damage trees? cont.
  • Mistletoes are also stingy with the nutrients produced in their leaves. The nutrients are translocated from mistletoe leaves and stems to the invading stem tissues at the point of connection with the hose but the nutrients are not passed to the host.
how long does mistletoe live
How long does Mistletoe live?
  • The longevity of the entophytic system seems limited only by that of the host and may extend to hundreds of years.
medicinal uses of mistletoe
Medicinal Uses of Mistletoe
  • Cherokee tribes used a "Tea ooze" to bathe the head for a headache, an infusion of the plant for high blood pressure, and lung problems, the dried, powdered plant, particular from the oak, for epilepsy, and to cure "love sickness", an infusion was taken after four days of vomiting.
medicinal uses of mistletoe cont
Medicinal Uses of Mistletoe cont.
  • Houma tribes used the decoction of the plant for debility and paralytic weakness, and as a general panacea.Modern medical research has shown that mistletoe has promise for treating some cancers, hypertension, vertigo, epilepsy, palsy and cardiovascular ailments.
medicinal uses of mistletoe cont60
Medicinal Uses of Mistletoe cont.
  • Various extracts from mistletoe are being investigated for treating cancer in humans, including ovarian cancer, lymphoma, and others. However, our mistletoe is very poisonous and should not be eaten or even nibbled.
medicinal uses of mistletoe cont61
Medicinal Uses of Mistletoe cont.
  • Research has also confirmed that it is, in fact, very poisonous, so alternatives were developed and mistletoe was not the miracle drug as some had believed.Traces of its use have even been found among Native Americans.
medicinal uses of mistletoe cont62
Medicinal Uses of Mistletoe cont.
  • Now the healing properties of mistletoe are being utilized in the fight against cancer with some interesting research and clinical trials showing that extracts of the

plant seem to have an inhibiting effect on tumor growth, and increase the plasma B-endorphin levels which directly affect pain and mood levels in patients undergoing chemo and radiation therapy.

how to control mistletoe
How to Control Mistletoe
  • The most effective way to control mistletoe and prevent its spread is to prune out infected branches as soon as the parasite appears. Remove infected branches at their point of origin or back to large lateral branches.
how to control mistletoe cont
How to Control Mistletoe cont.
  • Infected branches need to be cut at least one foot below the point of mistletoe attachment in order to completely remove embedded haustoria.
how to control mistletoe cont65
How to Control Mistletoe cont.
  • Mistletoes infecting a major branch or the trunk where it cannot be pruned may be controlled by cutting off the mistletoe flush with the limb or trunk. Then wrap the area with a few layers of wide, black polyethylene to exclude light. Mistletoe requires light and will die within a couple of years without it.
how to control mistletoe cont66
How to Control Mistletoe cont.
  • Some tree species appear resistant to broadleaf mistletoe. Bradford pear, crape myrtle, ginkgo, golden rain tree, sweet gum and sycamore are rarely infested.
how to control mistletoe cont67
How to Control Mistletoe cont.
  • Some people say that mistletoe should not be controlled. Clearly, mistletoes are part of the rich biodiversity and they play an extremely important role in the food supply of several native birds and insects. In any case Mistletoe causes very little damage.
the end
The End
  • All in all, when you bump into someone under a suspended sprig, there's a lot more to say than "Kiss me, you fool."
terms associated with mistletoe
Terms Associated with Mistletoe
  • Haustorium. The morphologically modified root which physically connects the parasite to the host. May be a primary haustorium if the radicle apex is directly transformed into a haustorium (e.g. Striga asiatica) or a secondary haustorium formed from tissues other than the radicle apex such as secondary root apices or from lateral positions on the root (e.g. Ximenia, Dasistoma). The haustoria of holoparasites are more complex (see Conopholis, Balanophora ).
terms associated with mistletoe cont
Terms Associated with Mistletoe cont.
  • Holdfast. In some mistletoes, a disc-like swelling at the end of the radicle that effects the first attachment to the host. In this example of an autoparasitic Macrosolen seedling, the holdfast is present and a young epicortical root is emerging from it.
  • Host. A plant that provides nutrition to an attached parasitic plant.
terms associated with mistletoe cont71
Terms Associated with Mistletoe cont.
  • Host-specific. A relationship whereby a parasitic plant successfully attaches to a limited number of host species.
  • Mistletoe. A general term for a parasitic plant that occurs on the branches of a woody host plant. Mistletoes occur in several taxonomically distinct families such as Viscaceae, Loranthaceae, Misodendraceae, and Santalaceae (incl. Eremolepidaceae).
terms associated with mistletoe cont72
Terms Associated with Mistletoe cont.
  • Parasite. A symbiotic association whereby an organism obtains at least some of its nutrition directly from another organism. In plants, a restrictive definition includes only parasites with haustorial connections to other plants, not mycotrophs. See also hemiparasite, holoparasite, facultative parasite and obligate parasite.
terms associated with mistletoe cont73
Terms Associated with Mistletoe cont.
  • Resistance. A feature or features of a plant that prevent it from serving as a host to a parasitic plant. This resistance may be manifested prior to or after initial haustorial attachment.
  • Sinker. See endophyte.
  • Susceptible. A feature or features of a plant that allow it to serve as a host to a parasitic plant.

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Joan Jackson is a Freshman at the University of Georgia. She is majoring in Agricultural Communications.

Dr. Frank Flanders is the Curriculum Coordinator for Georgia Agriculture Education. He and his staff produce the Georgia Agricultural Education Curriculum Resource and Reference CD annually.

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