|Poison ivy leaf shape. Two mittens on the sides giving a thumbs down with bilateral symmetry on middle leaflet.|
My original post on poison ivy from so many years ago focused on the diversity of poison ivy, but also the general form. It's amazing to me that we can identify a species from a thousand different angles under a thousand different lightings. No two poison ivy plants are the same size, shape, color, texture. But the patterns are distinct enough that our brain can readily generalize a specific form and lump it in with other similar forms and parse it out from dissimilar forms.
|Poison ivy with damage from a leaf miner|
Forging a search image requires spending 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 this can work, looking closely is more fun, more transferable, and more interesting. So, looking closely at poison ivy might reveal:
- A woody stem
- Each aerial stem typically has only 1-2 leaves emerging from it
- Alternate branched leaves
- Poison ivy that has taken to vining, at least in our region, is very uncommon
- When it does vine it uses aerial/adventitious roots to attach to tree (not tendrils, spiraling, or hooks)
- The 3 leaves are actually 3 leaflets that together form one leaf.
- Smooth (not waxy or hairy)
- Leaves often show signs of damage from leaf miners
- Form a T-shape, with two on side having short petioles (leaf attachments) than the middle leaflet
- Side leaflets are asymmetrical, middle one is bilaterally symmetrical
- Two side leaflets often look like they're given a thumbs down
- The fruits are like little whitish yellow pumpkins and readily pop off the stem
- They're often hidden beneath the leaves so difficult to find
- I've observed deer and catbirds eating them
- Reproduce mostly via runners (I've hand pulled poison ivy and if you get a runner you can pull up a few feet of horizontal roots!!)
- Roots are dark brown and around an 1/8"-1/4" in diameter at most.