The plant is American hogpeanut (Amphicarpaea bracteata). It is native to the eastern US. Here is a website with more info: http://plants.usda.gov/core/profile?symbol=ambr2
I include another photo. This plant is not a vine, it has woody stems which emanate from a thick matt of underground roots, which apparently is how it spreads. The stems stand upright and are woody except for new growth at the end of the stems. Thus I don't believe its hog peanut but a shrub of some sort. It grows in clumps and which stand alone and the stems don't climb or attach to anything. Any other ideas? Thanks so much...this is great fun for me, being able to ask someone instead of relying on field guides.
OK. If it is a shrub, it is probably Lespedeza, not sure about the species, maybe thunbergii.
Googled Lespedeza thunbergii imagesand there it was! Correct answer...thanks so much.