I looked at some Helianthus, H. laevigatus has a very short petiole but that appears to vary, the leaf venation doesn't appear to quite match.
This key might help once it flowers..
https://www.cals.ncsu.edu/plan...
http://plants.usda.gov/core/pr...
The petioles on this herbarium specimen are longer, but the venation running parallel or near to the lateral margins appears to be quite straight where the ID plant has 'bumps' for want of a better word.
http://bisque.iplantcollaborat...
