I didn't even notice the map but it for sure is all over Kentucky. I think I'm the only one I know who might not have an allergic reaction to it.
I also think there is a difference in the three plants just as Shoe mentioned, but here in W KY, they all are often commonly called by the same name: Poison Ivy. When I first moved here people looked at me like I was speaking a foreign language when I called a plant sumac and they called it poison ivy.
It could be because they all contain the irritating urushiol that causes the irritation, maybe?
