I took a picture of it on August 7, 2014 on the Wright’s Bluff Nature Trail at the Santee Wildlife Refuge. It is in the woody part of the trail (not the swamp or the migratory bird field). The other flowers that grow in this section are elephant’s foot and white mouth dayflower. I did not have an object to indicate size but it was a small plant.
I know this plant rather well – it is Sida rhombifolia, generally considered to be a weed, and generally thought to have been introduced from the tropics. It is in the family Malvaceae, the same family as Hibiscus.
Dr. Steven R. Hill, Botanist, SCNPS