It looks to be the root of the Louisiana Iris, Iris ser. Hexagonae.
I found a few websites that mention it but could not find it in my books. I cannot vouch for the absolute validity of these sites, and I believe the only way to find out for certain is to contact a voodosant in Louisiana who has knowledge of the plan associated with the root and can point you to it.
It's used in hoodoo also, and from Catherine Yronwode's Hoodoo Herb and Root magic it states the root is derived from several species, namely iris foliosa, iris fulva, iris hexagona, and iris tectorum.