Parasitic plants
Dodder
Parasitic plants derive all or part of
their water and nutrition from another
plant.
Parasitic plants may be classified as
being a holoparasite or a hemiparasite.
Holoparasitic plants produce no
chlorophyll and are totally reliant on
the host plant.
Dodder (Cuscuta) is a holoparisite, while
mistletoe (Phoradendron) is a hemiparisite.
Mistletoe
Hemiparasitic plants derive some of
their nutrition for the host plant, but
produce chlorophyll and are
functionally photosynthetic.
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Parasitic plants
Parasitic plants may also be grouped
as to whether they attach to the root
or stem system of the host plant.
Broomrapes (Orbanache sp.) is a genus of over
200 species of root-attached holoparasites.
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The orange flowers belong to the stemattached hemiparasite (Psittacanthus)
on a hardwood tree in Costa Rica.
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Parasitic plants
Parasitic plants attach to the
host plant’s stem or root through
a specialized structure called a
haustorium.
This creates a direct connection
between the vascular systems of
the two plants.
Dodder (Cuscuta)
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Parasitic plants
Parasitic plants must produce seeds
that can germinate in close proximity
to their hosts. Seeds in the root
parasite group are able to chemically
identify when a host plant is close and
trigger germination.
Stem parasites tend to produce fruits
that attract birds to move them from
host tree to host tree as in mistletoe.
The fruits contain a mucilage (called
viscin) that helps stick the seed to the
stem prior to germination.
Lysiana exocarpi
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Mistletoe (Phoradendron)
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Parasitic plants
Parasitic plants may associate with a number
of host plants or they may be very specific
about the host plants they colonize.
Juniper mistletoe (Phorodendron juniperinum)
colonizes junipers in western North America.
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Dwarf mistletoe (Arceutholium sp.)
colonizes several conifers,
including pines, spruce and firs.
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Parasitic plants
Root-attached parasites
In root holoparasitic plants, the only above
ground growth is usually the flowers.
Lathraea
Orobanche
Purple toothwort (Lathraea clandestina) is a root
holoparasitic plant with an attractive floral display.
It is parasitic on alder and willows as evidenced by
the spent willow flowers around the plant.
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Naked broomrape (Orobanche
uniflora) is a root holoparasite
from the relatively large
broomrape family.
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Parasitic plants
Root-attached parasites
Beechdrops (Epifagus americana) is a holoparasitic plant
specific to beech (Fagus) tree roots.
Beechdrops have the
interesting behavior of
producing open
(chasmogamous) crosspollinating flowers at the
top of the inflorescence
and closed (cleistogamous)
self-pollinating flowers at
the base of the
inflorescence.
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Parasitic plants
Root-attached parasites
By definition, holoparasites are also
obligate parasites, because they can not
exist without their host plant association.
Squawroot (Conopholis americana) is a
root holoparasite on oak (Quercus).
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Northern ground cone (Boschniakia rossica)
is a root holoparasite on alder (Alnus).
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Parasitic plants
Root-attached parasites
Indian paintbrush (Castilleja) is an example of
an obligate hemiparasitic plant. It produces
functional photosynthetic leaves, but is still
reliant on its host plant to grow successfully.
They mainly colonize grass species.
Indian paintbrush (Castilleja)
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Parasitic plants
Root-attached parasites
Pedicularis are also
obligate root-attached
hemiparasitic plants.
Elephant’s head grows in
moist areas in the Rocky
Mountains and is named
after the shape of the
flower.
Other Pedicularis have
the common name
lousewort. They are not
very specific about their
host plants.
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Lousewort (Pedicularis)
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Elephant’s head flower
(Pedicularis groenlandicum)
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Parasitic plants
Root-attached parasites
Some hemiparasitic plants, like these
false foxgloves, can grow without a
parasitic host association. They are
considered facultative parasites, but in
nature they usually retain a parasitic
association with a host plant.
Yellow false foxglove (Aureolaria virginica)
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False foxglove (Agalinis )
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Parasitic plants
Root-attached parasites
Sandlewood is an example of a woody
plant that is a root hemiparasitic plant.
Santalum lanceolatum
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Parasitic plants
Shoot-attached parasites
A major group of shoot parasites are
characterized as mistletoes. These are
aerial obligate hemiparasites.
Phoradendron californicum
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Phoradendron leucarpum
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Parasitic plants
Shoot-attached parasites
Shoot parasite flowers vary from being small and inconspicuous to very showy.
Phoradendron
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Santalum
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Psittacanthus
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Parasitic plants
Shoot-attached parasites
Following seed germination, an
attachment at the tip of the radicle
called a holdfast attaches to the stem
until the haustorial root can penetrate
through the bark and into the stem.
Mistletoe
seedlings
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Parasitic plants
Shoot-attached parasites
Some shoot parasites produce adventitious
epicortical roots that coil or travel along the
host plants stem and eventually establish
additional haustorial connections.
Haustorium
Epicortical
roots
Epicortical
root
Dendropemon
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Parasitic plants
Shoot-attached parasites
Dodder (Convulvulaceae) and Laurel dodder
(Lauraceae) are examples of vining holoparasites.
They form multiple haustorial connections as the
stems elongate and twist around the host.
Haustoria
Dodder (Cuscuta)
Laurel dodder (Cassytha)
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