There is a plant called Mexican petunia (Ruellia simplex) that blooms and then drops its flowers in a single day. It is, strictly speaking, a shrub but can grow up to four or five feet tall. It has purple flowers that resemble petunias. Here is a link to the Missouri Botanical Garden fact sheet on the plant so you can see if it resembles the plant you saw.

If that is not your tree, please email us with your photo so we can try to identify it for you: plantinfo@nybg.org.

Courtesy of NYBG Plant Information Service