An interesting observation. http://www.nature.com/news/2011/110318/full/news.2011.169.html?WT.ec_id=NEWS-20110322 Of course, once us amateur & enthusiatic gardeners get hold of a pretty introduction, it can turn invasive Real Quick!
The trick is trying to anticipate which plants are liable to explode in a given region, avoid establishing those. Probably this has never happened, even if an individual managed to accurately size a future nuisance plant up there would have still been the need to get everyone else to abstain from planting it in the as-yet non-infested region.
Not going to happen is it? I agree, Ron B. We still have garden centres & Home Depot selling "Lamiastrum", for goodness sake.
