An Itchy Lesson

Poison ivy, 3 June 2018 (photo by Kate St. John)
Poison ivy, 3 June 2018 (photo by Kate St. John)

Summer is the time for itchy things, especially poison ivy.  Here’s a timely lesson about leaves.

Do you know how to recognize poison ivy?  Here’s what makes it different:

  • Only 3 leaflets on the leaf stem. Never extra leaflets.
  • Lower leaves are lopsided; outer edge is longer than inner edge.
  • Leaves have notched edges, not saw-toothed.
  • Center leaf has a long stem. Side leaves have no stems.
  • No thorns at all.
  • Grows either on the ground or as a climbing hairy vine (the “hairs” are rootlets).
  • Its compound leaves are alternate on the main stem; noticeable on the vine. (The 3 leaflets make up a compound leaf.)

The slideshow below illustrates most of these characteristics.

On Throw Back Thursday: Learn more at this vintage article from 2009:  Look But Don’t Touch.

  • Poison ivy always has 3 leaflets, never more than that.


p.s. Most animals are immune to poison ivy.  Birds eat its berries. Deer eat the stems and leaves. Ladybugs and flies walk on it without any reaction!

Insects impervious to poison ivy's irritating oil (photo by Kate St. John)
Insects impervious to poison ivy’s irritating oil (photo by Kate St. John)


(photos by Kate St. John)

8 thoughts on “An Itchy Lesson

  1. Never noticed how the outer leaves are lopsided, good to know! I’ll often notice the “mitten” shape on some leaves as well, but certainly not always the case. Thanks for the review!

  2. Kate not related to this post but is there any update on how the peregrines chicks removed from downtown are doing??

  3. Kate – perhaps you would consider doing a PSA alongside poison ivy on Jewel weed and how you will often find it growing close to poison ivy. It’s a good antidote!

  4. I know poison ivy (and poison oak and poison sumac) well, but my wife Meg does not. She ran into poison ivy on our property last year (we don’t have the other two) and developed classic and nasty rashes. We just went through your site and the link with the tutorial on identification, and it was really helpful to her. Tomorrow is a field excursion to spot poison ivy on our property, but I think she knows the tell-tale signs well now. Thank you, Kate. Tony

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