All photos by Jim Mason
hen exploring the woods and fields of the Great Plains, a curious naturalist will usually
be on the lookout for dangerous animals such as skunks or venomous snakes, but might not
give any thought to the possibility of encountering a dangerous plant. Of course,
plants cannot "attack" a person, but some plants can cause harm if they are
touched. One plant that should definitely be avoided is Poison Ivy, and that can be
a real challenge because it grows in different forms, does not have a consistent leaf
shape and there are some plants in the same habitat that look like it!
Poison Ivy is a woody vine or sub-shrub that has a very wide distribution.
It may be found coast to coast from southern Canada to Mexico. It is also
known from the West Indies and China. It is a member of the Anacardiaceae,
or Cashew, family. Most members of this plant family have a tropical or sub-tropical
distribution. In North America, it is represented by the Sumacs (Rhus sp.),
Poison Ivy, Poison Oak, Poison Sumac and the Florida Poison Tree (Metopium
Poison Ivy is a nuisance because it contains a chemical that can cause the
skin of persons sensitive to it to develop a red, itchy rash and even erupt in blisters.
Urushiol is the active
ingredient in Poison Ivy that causes the rash and irritation. It is present in all
parts of the plant, but particularly in the sap. People vary in their sensitivity to
urushiol. Some have no problem with it and others experience severe allergic
reactions. This can also vary over the life of a person. You might be
unaffected as a child and become sensitized with repeated exposures. So even if you
are not allergic now, it is a good idea to learn how to recognize Poison Ivy in case your
body changes as you age.
The clinical name for the skin irritation caused by Poison Ivy is Rhus Dermatitis. It usually starts as itching and
small blisters within a few hours after exposure. Depending on how strong the
exposure was and/or how sensitive the person is, that may be all there is to it.
However, it may develop into an inflamed, swollen rash with open, weeping sores that
persists for up to two weeks. Severe cases may require a visit to the doctor.
Urushiol is absorbed into the skin within three minutes of exposure. If it is washed
off quickly with dishwashing soap and water, the consequences will be less, but you are
seldom close to a lavatory when you get exposed, so learning to recognize and avoid it is
the best strategy. An important fact to remember is that the urushiol can travel on
your clothes or the fur of your pets, so remember to wash them too if you suspect they
were in contact with Poison Ivy.
|The fruits of Poison Ivy are grapelike clusters of tiny, white,
pumpkin-shaped seeds with an off-white or pale yellow rind. The photo below was
taken in mid-November and shows that the rind dries out and flakes off eventually.
The fruits also contain urushiol, but that does not stop the birds from eating them!
Flickers and other woodpeckers are fond of them, along with sapsuckers, thrushes,
pheasants and quail. The rind provides food to the birds while the seeds usually
pass on through their gut unharmed and, in this way, birds are the agent for dispersal of
Poison Ivy seeds.
Poison Ivy berries
|Poison Ivy has variable leaves:|
|Poison Ivy has compound leaves.
That is, each leaf is made up of distinct parts, called leaflets.
In this case there is one leaflet at the end of the leaf stalk (or petiole)
and two leaflets opposite each other below the first. This is called a trifoliate pattern. The two lower leaflets have
very short stalks and are often shaped like mittens, with a lobe on one side.
leaves are not attached to the twigs directly opposite another leaf. This pattern of
leaf arrangement is called alternate.
The shape, color and texture of the
leaflets is highly variable. These shown on the right have fairly smooth margins,
but others may have rounded teeth or lobes.
|Several other plants look like Poison Ivy:|
All the following woody plants have trifoliate leaves and may be
found in the Great Plains.
Sumac (Rhus aromatica) Also known as Skunkbush, Aromatic Sumac
forms dense thickets up to 7 feet tall. It is native to the eastern half of the U.
S. and is often used for landscaping purposes and stabilizing eroding slopes.
In the wild, it will be found on rocky outcroppings and fence rows. Its berries are
red and densely hairy and form in dense clusters. While in the same family as
Poison Ivy, it does not contain urushiol.
Elder (Acer negundo) A member of the Maple family, Box Elder has
leaves that strongly resemble Poison Ivy in spring, but later in the year has leaves with
5 - 7 leaflets. Also, its leaves are directly opposite each other on the twigs,
while those of Poison Ivy are alternate. It becomes a medium sized tree and has the
typical paired, winged seeds that are common to Maples. It does not contain
Poison Oak (Toxicodendron toxicarium) The range of Eastern
Poison Oak includes eastern Oklahoma and the adjacent counties in southeast Kansas.
It is otherwise absent from the Great Plains. Its leaflets are smaller and have more
lobes than those of Poison Ivy and it always grows in a shrubby form. Its fruits are
similar to those of Poison Ivy, but usually hairier and larger. It does
contain urushiol and should be avoided.
||Poison Ivy leaves turn a vivid red color in
the fall. It is usually one of the first plants to change. This touch of
beauty on the landscape is, perhaps, a small repayment for all the misery it causes!
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- This page was spun by Jim Mason -
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Great Plains Nature Center
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Wichita, KS 67220-2200