Hi, Dr. Hill,
I know Helianthus are hard, so I hope photos will be enough to ID this one. Photographed Aug. 30 in a full sun ditch along a country road, clay soil, probably still Fall Line area. Leaves are opposite until near the top. What stands out to me is the overall light cast caused by the hairs on the stems and the unbranched nature, with flowers only appearing near the top. The flowers aren’t large, nor as small as the H. microcephalus you recently identified for me.
I think that the best match for this sunflower is Helianthus tomentosus. I don’t remember the leaves always being so truncate, but it actually keys out well, and is widespread in South Carolina in very sunny, somewhat dry areas.
Steven Hill, Ph.D., Botanist, SCNPS