Alex, a Wafer Ash (aka Hop Tree
Ptelea trifoliata ) is actually a shrub which prefers being "understory," shaded by a larger tree, fence, whatever. It is attractive, blooms in spring with small sprigs of white flowers that smell of vanilla, is a host plant for butterflies, and gets attractive little discs that contain a seed (children like to pick the discs and pretend they are coins). It is very hardy. We have three that we brought with us to the farm in one gallon pots, and the two that are shaded are at about 6' after 9 years. The one that gets more sun is at 7' and more dense.
Here is more information from an Illinois site (if it survives in Illinois, it shouldn't have any problem in Missouri!)
http://www.illinoiswildflowers.info/trees/plants/wafer_ash.htm