Several years ago I visited Itasca State Park and pictures of Poison Ivy
and Poison Oak were displayed for public viewing. The picture for "Poison
Oak" was really Virginia Creeper (Parthenocissus quinquefolia).
My botanical keys, Britton & Brown, lists Poison Ivy and Poison Oak as
separate species separated mostly by leaf shape. I've seen both leaf shapes
on the same plant. From my experience, I would challenge the idea of their
being separate species. I have traveled most of these United States and have
encountered only one plant that could, perhaps, be a separate species. It
was a California Poison Ivy that grew 12 to 15 ft. high, unlike its more
common cousin(?) that grows to about 2' high.
What is your experience on this subject?