I'm looking for help finding (the binomial of) the most tree-like species of cinquefoil and forsythia. I want something that tends strongly toward a single trunk rather than a multi-stemmed plant. Should I be looking at a cultivar of Potentilla fruticosa for the cinquefoil, or is there something that would better suit my needs (it's for bonsai)? How about the forsythia?

Thankyou for your consideration.

Al