I'm sorry to tell you that your butterfly bush is not a native plant. This news is sometimes shocking but still true. However, the jury is still out on whether it is an invasive or just a harmless ornamental. I haven't noticed butterfly bush invading woodlots and natural areas the way that bush honeysuckle does. In my garden it does reseed itself around the yard. A weedy shrub that only germinates in cultivated areas is not a threat to the environment, only to our gardens.
Last summer on my way to dinner I drove through Crondelet park and just happened to see a shrub clinging to the side of an abandoned building. At first I thought it must be a honeysuckle growing up there in such an inhospitable habitat but on closer inspection it had purple flowers. So I got out of my car and took some photos of the butterfly bush in it's strange habitat. The side of a building in not a cultivated space but this shrub was obviously thriving and ready to reproduce.
Have you noticed any butterfly bush that have escaped cultivation? Should we be worried about it invading natural areas? Should we be using it in our landscapes?
My neighbors had a huge bush in their yard and I did find several starts in my prairie. They were gracious enough to remove & plant back with natives. I also notified MDC.