Poisonous Plants

All you need to know about identifying poison ivy, poison oak, and poison sumac, as well as tips for treating the itchy rash they cause.

| Summer 2018

  • poison-sumac
    Poison Sumac (Toxicodendron vernix), Anacardiaceae. Detail.
    Photo by De Agostini / R. Portolese
  • poison-ivy-fall
    Poison ivy in fall.
    Photo by GettyImages/nameinfame
  • Poison-ivy-summer
    Poison ivy in summer.
    Photo by GettyImages/NoDerog
  • poison-oak-fall
    Poison oak in fall.
    Photo by GettyImages/Nancy Nehring
  • poison-oak-summer
    Poison oak in summer.
    Photo by GettyImages/kathyclark777
  • poison-ivy-path
    A path through the woods with poison ivy growing abundantly.
    Photo by Getty Images/dlerick
  • poison-sumac-fall
    Poison sumac in fall.
    Photo by Getty Images/photographer

  • poison-sumac
  • poison-ivy-fall
  • Poison-ivy-summer
  • poison-oak-fall
  • poison-oak-summer
  • poison-ivy-path
  • poison-sumac-fall

Europeans encountered many botanical treasures when they settled North America. Especially valuable were new foods they had never before experienced. But it didn’t take long for them to discover some less desirable plants as well.

The first written mention of poison ivy is found in Captain John Smith’s 1624 The Generall Historie of Virginia, New-England, and the Summer Isles. Even back then, “leaves of three, leave it be” was a useful verse to remember when spending time outdoors. It’s even truer today. Poison ivy is benefiting from increased levels of carbon dioxide in the atmosphere, and the plants are more numerous, more vigorous, and more potent than they were even a few decades ago.

Poison ivy and its cousins, poison oak and poison sumac, are known botanically as toxicodendrons. They contain an oil called urushiol that triggers an unpleasant immune reaction in 85 percent of the population. Every one of the lower 48 states is host to at least one of these plant varieties.

Poison ivy can grow as a climbing or trailing vine, or as a shrub, and is found in some form in most states. The West Coast is home to Pacific poison oak, which can grow as a woody shrub or a climbing vine, while Atlantic poison oak grows as a compact shrub throughout the Southeast. Poison sumac, a small tree, is found in wet, swampy areas in every state east of the Mississippi River. More rare than poison ivy and oak, poison sumac is also more toxic.

Recognition & Protection

The first element of prevention is familiarity with the plants’ appearances, which can vary widely. One encounter, or seeing one photo, won’t prepare you to recognize these plants in various settings, so it’s helpful to search online and study multiple photos taken at different times of the year.

For example, poison ivy’s three almond-shaped leaflets are usually glossy, but they range from light to dark green, and their edges can be smooth or notched. Poison ivy is easier to spot in fall, because the leaves are bright red. The leaves are shed by winter, but the off-white berries may remain, and the leafless winter vines may still be recognizable for their hairiness – but smaller offshoots may be hairless. Familiarity with all the possibilities is the best way to prevent exposure.



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