Sapindaceae

This is the genus used in commercial soap nuts (http://www.maggiespureland.com/), but it turns out we have a native species that grows from Missouri to Central America! The western form is hardy to Zone 6A! Apparently suckers a fair amount so watch out. S. saponaria is also used for soap though I do not know its quality.

To read more and find commercial sources check out: 

http://www.wildflower.org/plants/result.php?id_plant=SASA4