Found this plant blooming today Nov 11, 2013. Might be Gentiana latidens? Found near Fort Mill SC in thick woods, shady, and beside a small creek. Found no record of it in SC in my brief search online.
it is, indeed, a gentian. Gentiana latidens has also been called Gentiana saponaria var. latidens, but you are out of its range – it is found only in the Balsam Mtns of western NC. The flowers on yours are very wide, and this suggests Gentiana clausa, but, again, I don’t think that reaches SC. So, I would have to call it Gentiana saponaria which is the most common bottle gentian in the upstate, and the one I usually find there. Assuming you can open it, here is an article that clarifies the Gentians of the western Carolinas: http://www.bioone.org/doi/pdf/10.3119/C8-21.1
I hope this helps!
–Steven R. Hill, Ph.D. SCNPS