I recently purchased some property in Lexington County, SC. A few weeks ago I noticed this plant growing on a section of the property. Some are around 3 feet tall and spread around 1 1/2 to 2 feet. The area has sandy soil.
your plant is called the smooth rattlebox, Crotalaria pallida. It has also been called Crotalaria mucronata. It is often found along roadsides and in fields in the piedmont and coastal plain. It is in the bean family, but is not edible.
Steven Hill, Ph.D., Botanist, SCNPS