5- 6 feet tall, tiny blue/purple flowers, grows in weedy patches along fences, edge of woods, ditch banks. Much loved by bees, occasional butterfly. Stem is square in section.
(Leaf & stem photo is poor, but the best my camera can do. )
this is the introduced plant Verbena brasiliensis, which is spreading in South Carolina. It is very similar to Verbena bonariensis which has somewhat larger more attractive flowers. Both are vervains from South America.
Steven Hill, Ph.D. Botanist SCNPS