See M001 - M004 at http://www.flickr.com/photos/raphanus97/

I'm pretty sure it is in the Mimosa or "Bird-of-Paradise" subfamily of
the pea family. Alternate leaves length about 7mm. The plant is about
a meter high. The fruit is a small sphere (1mm diameter) that could be
divided into three parts. The flower is also very small (1mm across)
and probably consists only of 5 green sepals. I'm in the piedmont area
of South Carolina but that may be irrelevant because I've only seen one
specimen of the plant and I think it hitched a ride on the "plant-ball"
of a liriope that was transplanted from a nursery in a recent
landscaping.

Thanks in advance.