Jason,
That sure is a bueaty !
I don't think those are very common - they sure are not where I live (middle TN).
I know that Billy finds em like that occasionally up in the KY Mountains, but I think they just have some ideal seng growing conditions in the mountains and that probably lends itself to growth of extra foliage (leaves or prongs) like 5 prongs, or one leaf set with more than the standard 5 leaves.
Billy sent me a root from a plant that had extra leaves when he dug it, but this year it came up with just 5 leaves per leaf set, no extra's.
One of the roots I got from Billy has some small leaves on the berry stem, which is a little odd. Have never seen that in any of my local seng either.
Billy found one late last fall that had, best I remember 6 prongs, then a berry stem that went up about 10\" and had a big knot on it, with a bunch of stems and leaves running off it, then it went on up higher than that with another stem with berries. I think all together it had something like 16 prongs (counting those off that knot on the berry stem).
He put up some pics of it, it was sure a odd but extra ordinary seng plant.
TNhunter