These violets were accidentally introduced to our yard in suburban Charleston a few years ago, and are spreading about. I haven’t been able to ID the species (or could it be a hybrid?), but I did wonder if it could be Viola novae-angliae?
your violet does have some resemblance to Viola novae-angliae, which I do not know. However, that is a plant of the far north, and unlikely to be in South Carolina. I would have to call yours a form of Viola sagittata, which now includes several other species with similar leaves, such as Viola emarginata and Viola fimbriatula. Sometimes the teeth towards the base of the leaves are large, sometimes small, in this species. However, the fact that the leaves are more than 2x as long as wide most suggests Viola sagittata, the arrowhead-leaved violet. Your other images were much clearer than the one displayed here.
Steve Hill, Ph.D. Botanist, SCNPS