Watch out for poison ivy!

According to Jerry, my Michigan pharmacist brother, the second most frequent question pharmacies get after "What have you got for a cold?" is "What have you got for poison ivy?"  Contact with the plant commonly known as poison ivy may release urushiol, a toxin that can cause an itchy rash with weeping blisters in susceptible people.  Most people in the areas where poison ivy grows are allergic to urushiol or become allergic to it in their lifetimes through repeated exposure to plants that contain it. And while you can get poison ivy dermatitis at any time of the year from contact with urushiol, for those of us in the northern United States, our risk of being exposed to poison ivy likely increases in summer when we spend more time outdoors.  Being familiar with poison ivy can help you avoid it and the unpleasant consequences of coming in contact with it.  Increasing your awareness of poison ivy can aid you in enjoying your time outside with knowledge and without fear.

Although I had some minor skirmishes with poison ivy as a child, I realized how bad poison ivy could be in the summer of 1956 when Jerry had an extremely severe case of poison ivy all over his body, including on his genitals.  Jerry's poison ivy dermatitis was the result of exposure to poison ivy while working with our town's public works department between his freshman and sophomore years at college.  I remember feeling scared as I looked at him lying uncovered on a bed wearing only a pair of under shorts with an ugly red poison ivy rash and oozing blisters all over his body.  Mumbling a word or two, he seemed to be only semi-conscious.  Referring to this experience, Jerry recently told me, " I have never felt worse in my life, including when I was convalescing from surgery."  Because the rash was all over his body, it's likely Jerry got it from urishiol-filled smoke emanating from poison ivy being burned nearby.

Poison ivy, which is not an ivy, has a woody stem and occurs over most of the continental United States.  It can be confusing to identify because it takes different forms and grows in a variety of habitats.

Leaves and fruit

As a budding naturalist 18 years ago, I learned a mnemonic to help me remember what to look for in identifying poison ivy. 

Leaflets three? Leave them be.
Berries white? Run in fright.

The leaf of poison ivy has three asymmetrical leaflets on a long stem. Edges of the leaflets may be smooth, but usually have shallow notches. Leaflets often, but not always, are shiny or waxy on top.
 
Leaf color varies from dark to light green with some leaves having a reddish tint, especially when poison ivy is first leafing out.

A red-tinted leaf of poison ivy.

In fall, the plant's leaves turn a brilliant red, which unhappily could entice people to pick them for flower arrangements.

Poison ivy leaves beginning to turn red as fall approaches.

Other plants may have characteristics that resemble poison ivy and be wrongly identified as poison ivy.  The leaves of young box elder trees, which have 3-7 leaflets that may be asymmetrical like poison ivy leaves, are sometimes mistakenly thought to be poison ivy.

These leaves of a box elder sapling (Acer negundo) have three leaflets and, at first glance seem to be poison ivy.  Note, however, the leaves branch oppositely on the stalk, whereas poison ivy leaves branch in an alternate fashion.  Since the box elder tree is in the maple family, it also will produce the typical winged seeds of maple trees known as samaras.

Poison ivy's tiny, greenish flowers grow in clusters along a flower stalk and produce a creamy white, berry-like fruit.  Birds may eat the fruit and spread the seeds in their droppings.

Habitat and form

Poison ivy grows in a variety of habitats. It likes woodland edges, which is where I usually see it. All the photos for this article were taken in woodlands outside of Chicago.  But I also see it in sandy dunes that have some shade.  Once while birding, I followed two enthusiastic leaders across a sunny field of grass sprouting poison ivy plants.  While these plants were in full sun, woodland edges were nearby.  Perhaps poison ivy "likes" woodland edges because that's where birds frequently hang out, making woodland edges a likely place where poison ivy seeds will be sown via bird droppings.

Poison ivy occurs in diverse forms.  All forms of the plant are poisonous, and all parts of the plant contain urushiol, even for a time after the plant has died.  A dog brushing against poison ivy can get urushiol on its body and spread it to those who handle it.  To avoid getting poison ivy dermatitis, become familiar with all of its forms in your area. 

In spring, poison ivy emerges from the ground in hard-to-identify (and hard-to-photograph) thin, straight twigs that angle a bit and are 12 to 18 inches tall with a pointy, elongated, flattened bud at the top.  In our area, I often see these poison ivy twigs emerge en masse near a trail somewhat camouflaged by the previous fall's leaves still on the ground.  With the twigs looking so innocuous, it's easy for hikers to be accidentally exposed to poison ivy while absorbed in birding or enjoying spring wildflowers when they accidentally move off the trail to get a better view.

Poison ivy can be a vigorous ground cover.

The sun reflects off the waxy leaflets of poison ivy spreading itself along the ground.

The plant also grows as a vine twining around the trunk of a tree or on fallen logs.

Poison ivy entwines itself up and around a shagbark hickory tree.

Any nearby woodland tree can serve as a prop for the fast-growing vines.

A young wild black cherry tree supports a tangle of poison ivy vines.

Virginia creeper (Parthenocissus quinquefolia), another woody vine found in woodlands, is sometimes confused with poison ivy.  Like poison ivy, its leaves turn brilliant red in autumn.

Poison ivy in its "hairy rope" form climbs an ash tree.