Adams County Master Gardener
Now is the time of the year when many of us are venturing outdoors to work in our yards or walk in the woods. To protect ourselves, we need to be wary of various plants, such as poison ivy, poison oak, and poison sumac. While we use these three names interchangeably, they are not the same plants.
However, all three of them contain the chemical urushiol, which causes a rash when it touches the skin. It derives its name from urushi, a Japanese word meaning lacquer. The oil containing this chemical resides in the flowers, fruits, leaves, roots, and stems all year, even the fall and winter when these plants are dormant, and can cause a reaction
during any season. In fact, according to Susan Post of Center for Economic Entomology, the oil is active for a long time after the plant dies, possibly years.
An amount as small as a nanogram, a billionth of a gram, can cause a rash. However, responses vary greatly among individuals. The American Academy of Dermatology states that 15% of people are not allergic, while the U.S. Department of Health believes that up to 30% of people have no response.
However, when the oil touches the skin of sensitive individuals, the body tries to remove the irritant by producing histamines in the form of a fluid in blisters on the skin.
The chemical is so strong that it can be contracted by touching a pet that has rubbed against or rolled in a plant, grabbing the part of a tool that was used to cut it, or handling clothing that has brushed up against it. If these plants are burned, the oil becomes air born and can harm the eyes and lungs. Also, a reaction can develop if someone
contacts the oil on the skin of another person. However, the rash itself cannot be caught, because the fluid in the blisters does not contain urushiol.
The best protection is to avoid the plants and anyone or anything that has touched them.
Despite its undesirable attributes, poison ivy is an interesting plant. It is native to North America. John Smith was probably the first European to write about it. In 1609, he described it as "the poisonous weed, being in shape but little different from our English ivie; but being touched causeth reddness, itchings, and lastly blysters, the which
howsoever, after a while they pass away of themselves without further harme; yet because for the time they are somewhat painefull, and in aspect dangerous, it hath gotten itselfe an ill name." The name poison ivy may be attributed to him due to his comparison of it to English ivy.
Like many plants, it has a variety of common names. According to the book Just Weeds by Edwin Rollins Spencer, it is also called mercury, picry, poison creeper, poison vine, and three leaved ivy.
Despite its name, it is not a true ivy, hedera, which is a ground creeper or climber and has only two leaves.
While the saying, "leaves of three, let it be" is a good rule of thumb to avoid poison ivy, it only looks like it has three leaves. Actually, it has a compound leaf, which is defined as two or more leaflets attached directly to the same stem. In this case, poison ivy has three leaf blades in a trifoliate pattern: one leaflet at the end of the stem
and two below it that are directly across from each other.
It tends to grow at the edges of where humans live, work and play, sprouting in ground that has been disturbed. Unfortunately for us, it does not have any pests and requires little nutrition or water.
Also, it has three different forms in which it can grow. As a vine, it attaches itself to a tree, fence, or other lateral surface, by aerial roots, which support, but do not absorb nutrients or water. When the foliage is shed in winter, the roots are easier to see, helping to identify it out of the growing season. As a herbaceous plant, it does not
have a permanent wood stem. Many garden and house plants fall into this description. Finally, as a upright shrub, it has a woody stem and can grow quite large.
For more information about poison ivy, visit the website www.poisonivy.us
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