My goal with kiddos at Crow’s Path programs is to get them to be able to subconsciously identify poison ivy while they’re running around in the woods playing games. This definitely takes practice – lots of dirt time looking, drawing, studying – but once you create a search image and lock it into your brain, you no longer have to think to activate that process of identifying and then avoiding poison ivy. Awareness, to a certain degree, becomes a passive, embedded process.

Poison ivy leaf shape. Two mittens on the sides giving a thumbs down with bilateral symmetry on middle leaflet.
Poison ivy leaf shape. Two mittens on the sides giving a thumbs down with bilateral symmetry on middle leaflet.

Poison ivy leaf shape: Two mittens on the side leaflets giving a thumbs down with bilateral symmetry on middle leaflet.

Mash up of 100 poison ivy leaves

Above is a mash up of 100 photos I took of poison ivy leaves. The resulting image gives some sense of the essence or maybe Platonic ideal of a poison ivy leaf:

  • 3 leaflets in a T-shape
  • middle leaflet symmetrical, with longer petiolule
  • leaflets coarsely toothed
  • base of lateral leaflets quite variable

(I got the idea from artist Jason Salavon who does incredible mashups of all sorts of things, including the Simpsons, Playboy centerfolds, and special moments).

Poison Ivy ID Quiz

Sure, leaves of 3, let it be, but plenty of plants have 3 leaves (for most species these “leaves” are technically leaflets). Test your poison ivy identification skills with this ID quiz.

Forging a search image for poison ivy requires spending time lots of time looking closely (or I guess just subconsciously assimilating small bits of information over long periods of time works too as I don’t ever remember learning to identify dandelion or pigeons or Katy Perry, but here I am capable of recognizing her almost instantly on a poster at Staples). As much as the long game can and does work, looking closely is more fun, more transferable, and certainly more interesting. Below is what looking closely at poison ivy might reveal.

The zig-zag pattern of poison ivy twigs (Centennial Woods, Burlington)
Stem
  • A woody stem
  • Each aerial stem typically has only 1-2 leaves emerging from it
  • Alternate branched leaves
  • Can be a vine growing up the trunk of a tree, but, at least in our region, this is very uncommon and plants are usually short, unbranched shoots less than 24″ tall
  • When it does vine it uses aerial/adventitious roots to attach to tree (not tendrils, spiraling, or hooks)
Leaves
  • The 3 leaves are actually 3 leaflets that together form one leaf.
  • Smooth, often glabrous (glossy), but not hairy
  • Leaves often show signs of damage from leaf miners
  • Form a T-shape, with two on side having short petiolules (leaflet attachments; leaf attachments are called petioles) than the middle leaflet
  • Side leaflets are asymmetrical, middle one is bilaterally symmetrical
  • Two side leaflets often look like they’re giving a thumbs down
Male poison ivy flowers (Rock Point, Burlington)
The yellow, pumpkin-like fruits of poison ivy (Derway Island)
Flowers & fruits
  • Flowers are small, hidden beneath the leaves.
  • 5 white petals that curl backwards
  • Plants are dioecious (either male or female), only female plants develop fruits
  • Fruits are drupes (fleshy fruit with a central stone that contains a single seed)
  • Fruits look like little whitish yellow pumpkins; they readily pop off the stem when ripe
  • Fruits are often hidden beneath the leaves so difficult to find during the summer
  • Red-squirrels, gray squirrels, deer, ruffed grouse, cardinals, catbirds, and other animals eating the fruits and disperse the seeds
Poison ivy vine clinging to an old white pine trunk (Centennial Woods, Burlington)
Roots
  • Vining plants appear hairy, with hundreds of small adventitious roots clinging to the surface of whatever it’s vining up
  • Reproduce asexually via runners (I’ve hand pulled poison ivy and if you get a runner you can pull up a few feet of horizontal roots with over a dozen vertical shoots)
  • Roots are dark brown and around an 1/8″-1/4″ in diameter at most

More on the topic

Categories: Quizzes

Digging all this natural history content?

Become a monthly supporter on Patreon.

Be sure to check the archives for back issues.
And shoot me an email if you have an idea for a future blog post, newsletter issue, or podcast episode!

Subscribe to the Newsletter

STAY CONNECTED, LEARN NATURAL HISTORY