Ecology

Poison Ivy

Amanda Markle
Strawberry Hill Nature Preserve

(6/2022) As spring approaches and we begin spending increased time out in the great outdoors, our chances of encountering our dreaded three-leaf nemesis, Toxicodendron radicans, or poison ivy, increases. But wait, is this plant really our nemesis? No, not really. In fact, poison ivy (and its cousins, poison oak and poison sumac) are quite important to our natural world.

But, before we get into the details of poison ivy, just what is it? The first known reference to poison ivy dates from the 7th Century in China and later in the 10th Century in Japan. Though poison ivy was known to the Indigenous peoples throughout the Americas, it was not known to Europeans, as the poison ivy species did not grow in Europe. The explorer John Smith, leader of the first English settlement in Virginia, in the later 1500s and early 1600s, wrote one of the first descriptions of poison ivy. He noted the climbing appearance on trees similar to that of English ivy back home. Thus, originating the name – poison ivy. However, believe it or not, poison ivy is not a "true ivy," rather it belongs to the cashew and sumac family. Other members of that family include the mango, Peruvian pepper, and the pistachio. Poison ivy is native to both North America and Asia. Poison ivy can be found in every state except Alaska and Hawaii and is predominately found in the eastern and midwestern United States.

The visible characteristics of poison ivy are known by many – lobed or small toothed (not serrated) leaves found in bunches of three leaflets – inspiring the saying, "leaves of three, let them be." Leaves can be pointed or more rounded, large, or small. The compound leaves are alternate on the stem with each leaflet growing to become 5cm-10cm in length. Poison ivy has green berries in the summer with duller, waxy white berries in the fall. The leaves or usually red or shiny green in the spring and become a deeper green in the summer. As fall approaches, poison ivy leaves begin to turn a brighter orangish-yellow or red. Some larger, more mature poison ivy leaves can take on a mitten shape, with the outer leaflets having a deeper lobe (creating the appearance of a thumb) on one side. Poison ivy can grow as a small plant, shrub, or vine. Furry roots of poison ivy secrete a "glue-like" substance that helps adhere the roots to tree bark. Typically, the roots are brown in color and can run along the ground or climb the outside of a tree. Many times, the roots may be small and not noticeable on the bark of a tree. So, climbers beware!

Humans are aware of the poison ivy plant largely because of the itchy rash that one can get if exposed. The cause of the rash is the compound Urushiol. Urushiol is an oily mixture that causes an allergic reaction and a red and itchy rash; more specifically, urushiol-induced contact dermatitis. Urushiol is not an irritant that burns skin. Rather, the rash is a result of our own body’s immune system attacking our skin cells. Urushiol can stay on clothing and other surfaces for two years or longer unless it is washed away. Urushiol can be found in the sap of poison ivy throughout all the plant’s parts – leaves, flowers, berries, bark, roots, and branches. Most people have some allergic reaction to poison ivy. However, in the population, 15-25 percent of the population are not allergic to urushiol and have no skin reaction to poison ivy at all. Also, someone may be in contact with poison ivy several times without having a reaction and then begin developing reactions or "catching poison ivy" later in life after more exposures.

Poison ivy can typically last between 5-12 days, and in some cases, even longer. The reason most people believe that their poison ivy is "spreading" is because blisters may appear later than the initial outbreak. This is because an amount of the urushiol was in such a small concentration on that particular part of one’s skin that a dermatological reaction was delayed until a few days later. Once skin is washed and cleaned from an initial contact with poison ivy (and clothes cleaned as well), urushiol can no longer be spread on one’s skin. While many believe that the fluid in poison ivy blisters, if scratched and opened, causes the spread of the "poison," this is not the case. The fluid inside poison ivy blisters is produced by the body and does not contain urushiol.

So, how do we prevent or treat poison ivy? The best prevention is to know what poison ivy looks like and avoid it. However, if you must work around poison ivy or are hiking in areas where poison ivy is prevalent, wear appropriate clothing to protect your skin – long sleeve shirts, long pants, and gloves. Remember, urushiol can get onto your clothes and if touching your clothes before they are washed, urushiol may be transferred from your clothes to your skin causing a reaction as well. Never burn poison ivy. Burning the plant may cause the urushiol to become airborne where it can then cause skin reactions to the exposed parts of your body where the smoke has touched. If inhaled, the urushiol may cause breathing issues, which could become severe. Be careful petting a dog or cat after they have been in poison ivy. While they cannot get poison ivy (neither can most animals or birds), the urushiol may be on their hair or fur, which can then be transferred to a person. If known or suspected contact with poison ivy has been made, wash your skin with soap and water as soon as you can to remove any urushiol. Over the counter skin treatments are available for a poison ivy rash and one can seek guidance from a licensed medical professional.

As mentioned previously, the poison ivy plant has benefits in the natural world as well. Poison Ivy is eaten by many animals and birds. Black bear, deer and racoons eat the leaves and stems of the plant. Deer, especially, depend on poison ivy leaves as a food source. For many of these animals, poison ivy’s "eye-catching" fall colors of red and orange are a sign that a good food source is available. Also, a birds feed on poison ivy berries: tufted titmice, American robins, woodpeckers, wild turkeys, crows, and quail. Poison ivy provides ground cover for smaller animals, reptiles, and amphibians - such as squirrels, chipmunks, lizards, and frogs.