V. I googled and found a site set up by a woman in MA with lots of info and links. She also has germinated seed from the variegated plant. Seems there may be some hybrids being found too.

That site has a photo of a red pickup truck being "attacked"...reminds me of our southern menace kudzu. Good luck with your research. josh

Here is a link that might be useful: Japanese Knotweed

Did you ever find out? Do you still have your 'variegata' plants?

I have 'Variegata' too and I just recently removed some young plants from a sunny spot where I felt it was too happy. I found shoots coming up several feet away. Hope I got all the shoots!

I still have 2 plants in a shady dry spot that seem very well behaved, but the more I read about this plant, the more I think I should destroy it all while I have the chance (I hope).

I have the "compacta" variety and have been happy with it until I read how problematic the species can be. In my old house it was about ten years old and the patch it had spread (from a 1/2 gallon pot) was about 4'x4'. It was a lovely plant in the garden, with lots of bright greens and reds and a great structure to it. I've now planted it in a shady spot in our new house, and I'm wondering if I've made a mistake....

There seems to be confusion in this thread between "invasive" (aggressive proliferation causing significant displacement or harm to native populations of plants
and/or animals) and "aggressive" (rapidly spreading growth in a localized area). Just because you don't see a plant colonizing the area near where you planted a specimen, doesn't in any way mean it's not invasive and causing problems. Also, just because you do, doesn't mean it is invasive.

One reasonable way to make a decision about whether, in regards to potential for invasiveness, a plant should be planted in a particular area (state, part of the country, etc) is to review reports from appropriate state agencies or organizations like Exotic Pest Plant Councils. If a plant is reported to be an invasive problem in your area, then planting it is probably not an an environmentally responsible thing to do. If, on the other hand, there is no issue anywhere around your (in your part of the country), then plant away and enjoy.