Growing in SC dry, sandy soil–in the pea family?
no, not in the pea family, it is in the snapdragon family, Scrophulariaceae. Your nice wildflower is Agalinis setacea, the threadleaf false foxglove. It is rather widespread in our area in this dry sandy soil in full sun. The plant tends to be tinted reddish. The flowers all tend to fall off at the end of the day.
Steve Hill, Ph.D., Botanist. SCNPS