Ask Mr. Smarty Plants

A four-angled stem (square) suggests one of two plant families—Family Lamiaceae (Mint Family) or Family Verbenaceae (Verbena Family).  Since the Verbena family is smaller, let's start with it first. On our Native Plant Database page select Verbenaceae (Verbena Family) from the Family: slot in the green Search native plant database: box.  This will give you a list of 48 plants and you can use the NARROW YOUR SEARCH option to limit the list by choosing "South Carolina" from the Select State or Province slot and then select "Blue", "Purple" and "Violet" from the Bloom Color slot.  This will limit the list to 8 species that you can scroll through.  The two from this list that look like candidates to me are:

Verbena bracteata (Bigbract verbena)

Verbena hastata (Swamp verbena)

You should do the search yourself to be sure I didn't miss a possible candidate for your plant.

If you do a similar search by choosing Family Lamiaceae (Mint Family) from the Family: slot in the green Search native plant database: box, you will get a list of 178 plants.  Using the NARROW YOUR SEARCH option described above, your list is reduced to 33 plants.  You will notice that some of the species don't have photos available (e.g., Clinopodium georgianum (Georgia calamint).  However, if you click on the link to the species and scroll to the bottom of the page to the ADDITIONAL RESOURCES area and click on the species name beside Google:, you can links to other webpages about the species that have photos.  There is one on that list that looks like a candidate to me:

Prunella vulgaris (Common selfheal)

Again, you should do the search yourself to be sure I didn't miss a likely candidate.

All the plants in our Native Plant Database are, indeed, native to North America.  If the plant you saw is a garden escapee, it is very likely an introduced cultivar and would not appear in our Native Plant Database.

If none of the plants from the above searches is your plant and you have (or can take) photos, please visit our Plant Identification page to find links to several plant identification forums that will accept photos of plants for identification.