How to Identify Iowa’s Poisonous Plants
Posted: 08/22/2014

“Leaves of three, let it be.” Many of us had this mantra drilled into us as children, and we continue to repeat it when we venture into the woods today. However, we shouldn’t let it scare us out of the woods altogether. Learning to identify Iowa’s poisonous plants can help you steer clear of rashes, blisters and itchy, painful skin.

While a number of Iowa plants can be harmful to eat, only a handful cause allergic reactions when we touch them. The most common culprits are poison ivy, wild parsnip and stinging nettles. Keep in mind that poison oak and poison sumac do not grow in Iowa (see below).

Identifying poison ivy and other poisonous plants from the Iowa DNRPoison ivy
While some people like to brag that they can roll around in the stuff without seeing a single welt, many people will have an allergic reaction with itching, burning and blisters that develop within 12 to 24 hours after coming in contact with the plant’s oil. You might not have a reaction the first time you come in contact with poison ivy, but roughly 85 percent of people will react the second time.

If you think you’ve had a brush-up with poison ivy, thoroughly wash your skin with soap and water as soon as possible. Leave shoes outside and wash clothes separately, as the oil can remain on surfaces and cause new flare-ups when you come in contact with it again (but the rash itself is not contagious). It can also remain on a pet’s fur without bothering the animal, so be sure to give Fido a good bath too, so you don’t break out from petting him.

Poison ivy can take many forms, but when you learn to identify it, it can be easy to avoid. It’s not the only plant with three leaves, so look for shiny or dull leaves that are 2 to 5 inches long. And actually, it’s three leaflets comprising a single leaf, not individual leaves. The stem won’t have thorns or look fuzzy. Poison ivy can grow as a small plant, shrub or as a vine climbing a tree. The plant blooms in the spring and has white berries from late summer through winter. Rabbits and other wildlife love snacking on the berries and plants. 

Identifying wild parsnip and other poisonous Iowa plants from the Iowa DNR

Boxelder can look similar to poison ivy, but its leave are opposite each other on the stem, while poison ivy leaves alternate along the stem. Young boxelder leaves can have three leaflets, but older ones on the same plant will have five. Boxelder twigs are green or purple while poison ivy twigs are brown.

While it might be tempting to burn off a patch of poison ivy on your property, the oil remains in the smoke, allowing people to inhale the oil into nasal passages and the lungs. Never burn poison ivy.

Wild parsnip
Flowering from May to July, the non-native wild parsnip plant has lacy, yellow-green heads. If its oil touches the skin and then is exposed to sunlight, painful blisters will develop. Often found in great crowds in road ditches, avoid using a lawn string trimmer to remove it, as you’ll get splattered with broken parsnip tissue and have a high exposure to its toxin.

Stinging nettles
This plant does just what its name advertises – as you brush up against it, plant hairs inject acid into your skin, like a syringe giving a shot. However, the skin’s reaction is milder than with poison ivy or wild parsnip, and it usually clears up within just a few minutes. 

Found often in woodlands near streams, the plant can grow from 6 inches to 6 feet tall. The stinging nettles are found on the stem of the plant, which is stiff. Leaves grow opposite each other on the stem. However, the wood nettle plant has alternate leaves and grows in shaded forests, but will sting you just the same as the stinging nettle.

How to avoid stinging nettles and other poisonous plants | Iowa DNR

No poison oak or poison sumac in Iowa

Poison ivy (Toxicodendron radicans and Toxicodendron rydbergii), poison oak (Toxicodendron diversilobum and Toxicodendron pubescens), and poison sumac (Toxicodendron vernix) all contain the same toxic oil named urushiol, which causes a red, blistering, itchy rash. This common thread can lead to the assumption that you've had a brush up with any of the three, but having a rash does not by itself indicate which species you encountered. 

Poison ivy is very common in Iowa, but poison oak and poison sumac have never been documented by botanists in the state. Maps of plant distribution 

Disagreements about which species occur in Iowa has to do with the difference in the way that botanists and the most people classify these species. Botanists use the terms is a narrow sense that applies the name “poison ivy” to two species that do occur in Iowa and restricts the names “poison oak” and “poison sumac” to species that do not occur in Iowa.

Many other people in contrast, use these same names in a much broader sense, applying the terms “poison oak” and “poison sumac” to what botanists would classify as poison ivy. Arguments over the use of common names of plants can be never-ending because so many people call the same plant by different names. This is why scientific names (the italicized Latin names that follow the common name in parentheses) are more useful for precise discussions. In this article, we are following the narrow sense used by botanists.
Comparison photos illustrating the differences recognized by botanists 

In Iowa, fragrant sumac (Rhus aromatica) may be often confused for poison oak, but it's not poisonous. It also grows in the same habitat as poison ivy - possibly leading people to get a rash from the ivy, then mistakenly attribute it to the plant they saw that resembles poison oak. Botanically, the genus Toxicodendron (which contains poison ivy, poison oak and poison sumac) and the genus Rhus (which contains the true sumacs) are in the same family, so they bear a resemblance to each other.  However, only the Toxicodendron species are poisonous, the Rhus species are not (except for especially sensitive people). 

While Iowa has some poisonous plants, don’t let it keep you out of the woods. Stay on groomed trails and paths until you feel confident in your identification skills.