Invasive Weeds from Alaska
There are many types of Spiraea, from much of the Northern Hemisphere. There are shrubby forms as well as some that are Herbaceous, such as our own native Meadow Sweet, although that has since been re-classified as Filipendula.
Many well behaved garden varieties exist, which never cause any problems, but this one is a real nuisance. On the picture above; clearly irresponsible people have dug it up from their gardens and just lobbed it onto the land behind, where it has began to try and engulf the whole site.
Spiraea douglasii is a highly invasive species of this genus. Spreading aggressively from underground roots. It is native to western North America from Alaska, across southwestern Canada and the Pacific Northwest, but not here!