How certain are you that your plants are correctly named Kent?
Eutrochium purpureum : "margins coarsely serrate"
http://www.efloras.org/florata...
For a live example of coarsely serrate, see Coreopsis latifolia leaves near the bottom ..
http://www.namethatplant.net/g...
E. purpureum leaves:
http://www.namethatplant.net/g...
Eutrochium fistulosum: " finely serrate (teeth rounded, blunt)"
http://www.efloras.org/florata...
The teeth on these plants are definitely rounded and blunt.
The leaf margins do match the line drawings, however it might be another species altogether!
The examples shown on the Carolinas & Georgia site don't match E. fistulosum, assuming they are correct.
More examples ..
http://gobotany.newenglandwild...
http://gobotany.newenglandwild...