Explains how to identify poison ivy, poison oak and poison sumac, using identifies for their leaf shapes, colors, stems and growing habits.
How to avoid the rash
The active ingredient in poison ivy, poison oak and poison sumac is urushiol, an oily mixture of organic compounds with allergenic properties. It can hang on your tools, clothing, shoes, or a pet’s fur, but soap and water will easily remove it. However, be aware that if you don’t wash these items, the urushiol will remain on them and can be transferred from them to your skin.
You can also wash it off your skin if you wash the affected area with soap and cold water almost immediately, and scrub it hard with a washcloth. This can be difficult, especially if you didn’t even know that you even touched any of these plants. If you don’t, it will penetrate the epidermis in minutes. Once this happens, no amount of wash will stop the inevitable rash and itching.
Another fact about poison ivy, poison oak, and poison sumac is that contact with them can be riskier in winter than in summer. The winter risk is that the plants will be deciduous, which means they will drop their leaves, which is one of the most important ways to identify them.
A third is that all three are mainly eastern plants. There is a different type of poison ivy in the western United States. That is why poison ivy is sometimes referred to as eastern poison ivy. It is widespread and can reach as far as Canada and Newfoundland.
Here’s an ID guide that gives some more pointers to keep your time outdoors comfortable and itch-free.
How to identify poison ivy (Toxicodendron radicans)
As the poison ivy gets older, the leaves turn from light to dark green.
Poison ivy is by far the most common of the three. It grows in a variety of habitats and is basically everywhere. What sets it apart from poison oak and poison sumac is that it can take on different forms of growth. It can be a small shrub, it can crawl across the ground and it almost like a ground cover can climb into surrounding shrubs or a tree. Here’s how to spot it in each of its different forms.
First look at the leaves. You have no doubt heard the saying “leaves of three leave it” or some variation of it. The saying applies to all poison ivy growing habits in general, but it is botanically correct for none of them. Poison ivy doesn’t have three leaves, although that’s what most people call it. Instead, it has leaves that are made up of three leaflets. Look closely and you will notice that the leaf has two side leaves that are directly connected to a central stem and a third leaf, the end leaf, which is at the end, on a small stem-like extension.
There are several other lesser-known features of the leaves that will help you identify poison ivy. One of these occurs in the spring. When the plants first leafed, they will have a brownish-red tinge to the tips of the new foliage. When the leaves mature, they almost always turn deep green rather than light or light green. Often the leaves also have a slight sheen, although this is not always the case.
One feature of the leaves that is not a reliable identifier is the shape of the edges. In some cases the edges are jagged (serrated, botanically speaking) and in others they are smooth.
Another warning about poison ivy is the beautiful hues the leaves can take on in autumn. The colors can range from red to yellow to orange. When you’re in the woods collecting leaves for arrangements, be careful not to add these to your haul.
There is one other plant that is sometimes mistaken for poison ivy. That is Boxelder maple (Acer negundo). At first glance, boxelder maple looks like poison ivy because it has three leaves. But there is an easy way to tell the difference. Take a close look at how the leaves are placed along the stems. In boxelder maple, the leaves are exactly opposite each other. In the case of poison ivy, they alternate or are offset along the stem. It’s a really, really good way to tell the difference.
The vine and roots
There is also a tell-tale way to identify poison ivy when growing as a vine. In this form, the vine can resemble a hairy rope, forming very hairy roots that help it cling to the tree’s bark. Botanists call these random roots, which simply means that roots grow where you normally wouldn’t expect roots to grow – in this case, from the trunk of the vine as it climbs up the tree.
Often times, you will see that once the vine is attached to the tree, the branches of the plant actually protrude four to five feet in a horizontal pattern. As with poison ivy, which grows as a shrub or ground cover, poison ivy vines also have three leaflets.
The ropey look has led to another saying about how the casual observer can identify poison ivy when growing as a vine: Bark like a rope, don’t be a dope. However, the rope-like appearance of the stem is not a reliable way to identify a poison ivy vine in winter.
Native climbing hydrangea, sometimes called the wood vampire (Decumaria barbara), is another native plant that grows as a grapevine and also has a stem-like stem. Climbing hydrangeas are easily recognized from spring to autumn by their rounded leaves or cream-colored flowers that appear in small clusters. Determining the difference between it and a poison ivy tendril in winter (when there are no leaves to distinguish them) is a whole different matter.
Another way to help the casual gardener, homeowner, or hiker identify poison ivy is through the clusters of berries the plant produces. At first they are green, but when they mature they turn white with a waxy coating. The berries are about the same size as those on Beautyberry (Americana callicarpa), although the shrubby Beautyberry has nothing to do with poison ivy. Poison ivy berries are an important source for songbirds that will not be disturbed by the urushiol, and help the plant spread in its feces through undigested seeds.
As with many plants, there are anecdotal stories about poison ivy that may or may not be true. One related to poison ivy is that when it grows as a vine, its leaves can sometimes mimic those of the host plant. However, we could not confirm scientific evidence of this.
How to identify poison oak (Toxicodendron pubescens)
The poison oak only grows a few feet tall and is not a vine like poison ivy.
Poison oak is nowhere near as common as poison ivy. Poison oak is also found in tripleaf, but what makes it difficult to distinguish from poison ivy is that its leaflets look exactly like those on poison ivy. In other cases, the leaflets resemble a white oak leaf, from which the plant gets its common name.
There are several growing habits that can help differentiate between poison ivy and poison oak. One of them is that it generally like to be drier than where you see poison ivy. The other thing is that poison oak does not climb. The tallest it gets is a foot or three. You will never see it climb a tree as a vine.
The only really unique identifier about poison oak because it can look something like poison ivy is you sometimes see the oak leaf shape.
The point is of course retained regardless of the leaf shape. “Leaves of three, leave it be” unless the leaflets are opposite on the stem. If the leaflets are staggered, regardless of whether they are the tell-tale oak shape, the painful itchiness is the same when you come in contact with it.
How to identify poison sumac (Toxicodendron vernix)
Of all three poisonous plants, the poison sumac grows the highest; but it is unlikely that you will encounter it.
The last in the trio of poisonous plants doesn’t look like the first. Poison sumac can grow into a large shrub or small tree that can grow up to eight or ten feet tall and produce numerous leaflets, with each leaf having up to 10 or more leaflets. It has the furthest westerly range of the three and can grow as far as Texas.
You will usually not see poison sumac where it is dry. It grows on the edges of bogs, seepage or swamps. In addition, the central stem of the poison sumac, which contains all the leaflets, is often reddish.
This is one that should definitely be avoided. Poison sumac causes the worst reaction of the three. Fortunately, like poison oak, it is not a common plant and people are unlikely to come across it unless they spend a lot of time in the field.