When I first moved here I was alarmed by the amount of poison ivy I found growing in my woods. I later discovered that I had a poison ivy look-alike. I have poison ivy too, but it’s not nearly as prevalent as I first thought. The look-alike is really wild sarsaparilla (Aralia nudicaulis). They don’t look too similar when they are grown, but when they first emerge, they are pretty hard to distinguish. Compare:
The sarsaparilla will often have five leaflets in a cluster; three at the end of the stem a la poison ivy, and two more bringing up the rear guard. Their fruits and flowers are pretty different too, but I didn’t take any shots of that today, on account of how I couldn’t find any mosquito repellent, and didn’t want to spend too much time out there feeding those brutes. Black flies too, actually.
The sarsaparilla sports its blossoms on the end of a separate stem that comes up from the same point as the main stem. These blooms are held beneath the leaves and form an umbel. The poison ivy blooms (and thus fruits) share a stem with the leaves.
Note how they are both reddish when young. They both go green within a few weeks of emerging.
Update: here’s another photo to try to answr Mark’s question: