Buttonbush (Cephalanthus occidentalis
) looks like an interesting plant to try. This plant is a member of the coffee family (Rubiaceae) and grows in swamps in the Eastern US, Mexico and the Caribbean and it blooms with very pretty white globe flowers. I wondered if this plant would be suitable ofr growing indoors--a lot of native trees and shrubs won't grow inside--but I found several references to keeping it as indoor bonsai. One picture that I encountered even showed a bonsai plant only about 16" tall with several flowers on it.
(Wikimedia Commons image: http://en.wikipedia.org/wiki/File:Ce...cidentalis.jpg