Me again...We have sweetspire (itea) cultivar 'Little Henry', some from Musser, some from Lowes. The oldest are 4-5 years, about 3' x 3'. They do sucker, and also will self-layer, but I don't think their behavior is invasive. I WANT mine to increase, because I need to cover another area. They are also pretty easy to start from cuttings.

I have Little Henry and it has not moved much but where I work there are larger plants, I believe they are the species and they have moved quite a bit. In fact the gardeners removed the mulch and you can see the suckers spreading out and then rising up. They will be very bushy, maybe 5-6 feet wide in a few years.