Hi, Dr. Hill,
This plant, photographed on July 4, lives at the edge of a swampy area in the Fall Line, partly shady. It has a hollow stem (less than 3/4-inch diameter) with milky sap. Some of the leaves have a slightly red midrib. Periodically along the edge of the leaf are tiny, sharp points. The bottom side of the leaf is lighter green than the deep green top side. The plant was broken at the main stem, so I don’t know how tall it would have gotten, but it is at least 4+ feet tall.
this plant will be much easier to identify when it is in bloom. It appears to be a Prenanthes in the Aster family, based on the leaves. While I am tentatively calling it Prenanthes alba, it may be confused with P. altissima (tall rattlesnakeroot); P. alba has 8 primary bracts, P. altissima has 5. It may also be confused with several other species.
Many have moved this into another genus, Nabalus. It is closely related to Lactuca, lettuce.
Steve Hill, Ph.D., Botanist, SCNPS