Zigzag Spiderwort, a native species, has been added to the USWildflowers database (09/10/2010.)  Scientific name is Tradescantia subaspera.  Another common name is Wideleaf Spiderwort.  Photo below was taken at Reflection Riding in Hamilton County, Tennessee on Sep 6, 2010.

Zigzag Spiderwort, Wideleaf Spiderwort - Tradescantia subaspera