Mistletoe

1
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

Click HERE for more information about the authors.
2
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.

3
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.

4
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.

5
Mistletoe is a Thief

• Its 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.

6
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.

7
What is Mistletoe cont.

• Evergreen clumps of mistletoe are readily
  observed on deciduous trees in winter when leaves
  are off the trees.

8
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.

9
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.

10
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.

11
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.

12
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.

13
The Sex of Mistletoe

• Mistletoe plants are either male (produce only
  pollen) or female (produce berries).

14
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).

15
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.

16
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.

17
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.

18
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.

19
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.

20
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.

21
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!

22
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.

23
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.

24
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.

25
Traditions of Mistletoe cont.

• Because of its association with pagan
  ceremonies, mistletoe was banned from Christmas
  ceremonies by the Church in Medieval times.

26
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.

27
What Genus/Species is Mistletoe?

• The mistletoe that is commonly used as a
  Christmas decoration, genus Phoradendron
  flavescens, is native to North America.

28
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.

29
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.
30
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.

31
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.

32
Seed Dispersal cont.

• 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.

33
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.

34
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.

35
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.
36
Germination

• 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.

37
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.
38
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.

39
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.

40
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.

41
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.
42
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.

43
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.

44
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.
45
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.

46
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.
47
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.

48
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).

49
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.

50
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.

51
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.

52
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 trees life span, damage can be significant,
  but not noticed by humans for years to come.

53
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.

54
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.

55
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.

56
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.

57
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.

58
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.

59
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.

60
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.

61
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.

62
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.
63
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.

64
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.

65
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.

66
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.

67
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.

68
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."

69
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 ).

70
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.

71
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).

72
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.

73
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.

74
Would you like to play a game?
YES- I would like to play How would you like to
be a Mistletoe Millionaire (Game 15)
YES- I would like to view the questions in
Microsoft Word.
NO- I would like to end now.
75
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.
Click here to return to the first slide.