It’s out there crawling up trees.
It’s in the grass.
It has almost unnoticeable “thumbs” on the bottom two leaves.
It has Very obvious “thumbs” on the bottom two leaves.
It’s creeping in the ditch.
It’s wearing red instead of green.
There is the climbing variety (toxicodendron radicans)
and the non climbing (toxicodendron rydbergii) or Rydberg's poison ivy.
They interbreed, look very similar, sometimes grow in the same places, and give you the same rash. So who really cares about the difference.
When was the last time you got poison ivy? or are you one of the lucky people who just don’t get it?