Transcript What is Mistletoe cont.

Mistletoe
A Special Lesson
Produced by: Joan Jackson & Dr. Frank B. Flanders
Georgia Agricultural Education Curriculum Office
April 2002
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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
 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
 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
 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?
 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.
 Evergreen clumps of mistletoe are
readily observed on deciduous trees in
winter when leaves are off the trees.
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 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 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?
 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.
 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
 Mistletoe plants are either male (produce
only pollen) or female (produce berries).
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?
 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

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.
 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 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 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 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 “lifegiving” power.
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 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 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.
 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 cont.
 Because of its association with pagan
ceremonies, mistletoe was banned from
Christmas ceremonies by the Church in
Medieval times.
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?
 The mistletoe that is commonly used as a
Christmas decoration, genus Phoradendron
flavescens, is native to North America.
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

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.
 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 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 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.
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 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 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.
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.
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 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 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. Wedgeshaped projections called
sinkers grow from the cortical
strands and pass through the
cambium to the outer surface
of the lignified xylem.
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 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?
 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.
 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?
 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.
 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? 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? 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? 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? 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? 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.

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? 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? 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?
 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.
 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? 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?
 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
 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.
 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 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 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 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
 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.
 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 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 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 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.
 All in all, when you bump into someone
under a suspended sprig, there's a lot more to
say than "Kiss me, you fool."
The End
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.
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 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 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 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.
Would you like to play a game?
YES- I would like to
YES- I would
play “How would you
like to be a Mistletoe
Millionaire” (Game 15)
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Microsoft Word.
NO- I would like to
end now.
Joan Jackson is a Freshman at the
University of Georgia. She is
majoring in Agricultural
Communications.
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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.