Ok, normally I can figure stuff out on my own. I think this one is a traveller...I thought at first that it was Eupatorium Rugosa, but the flowers are nowhere near the same, and the leaves are very waxy rather than slightly flat like most specimens of "chocolate" I've seen.

I know the pictures below are not great, it came up near my ferns and oak leaf hydrangeas on the north side of my house, so it's hard to fully see the plant. We transplanted to a pot when it started flowering this weekend (just in case it's prolific self-seeder!), so I can get better pictures if it will help.

Basic info:

Currently 36-42" tall and I believe it is at full maturity.

Seems to prefer shady, moist soil. Stem sample wilts within minutes of picking it, or during dry spells.

Root system is very shallow, stem is soft (bordering hollow) in its chamber. Very weed-like, actually.

Stem structure is ascending, and as you may not be able to see, at each primary (and secondary?) stem segment, 2, 3 or more stems grow outward from it.

Leaves are very thin and waxy, serrated edge (as shown) intensely purple at the tips especially; end leaves are deep, deep purple while other leaves are green. The plant itself is gorgeous, a real shower.

Stem is smooth but vertically ridged, varying from square to hexagonal in shape.

The final flower/seed pod is VERY similar to anise hyssop in nature (except square and the diameter of a BB), but the flowers are insignificant little purple dots on each of the four corners of the pod.

The flower grows from the end of the stem slowly (terminal bud), it grows out one link at a time, almost like vertebrea, when it reaches an end length of 1-1.5" in length, it gets a light fur to it, then produces the tiny purple flowers at each corner from end to end.

Any help to ID this is greatly appreciated. I've talked to every local nursery that would typically know everything, and nobody can pin this. I've done everything shy of contacting the extension service.

So, is this a weed, a plant or what? I am going to keep the seed pods, but have it as far from my other plants as possible until I can ID it.

Pictures:

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