The photo above is from the USDA PLANTS database. I did not grow this lovely specimen of eupatorium album (white thoroughwort), but this species, or one that looks a lot like it, has been an enthusiastic colonizer in our meadow garden this summer.
The purple-flowering plant in the photo to the left is one I brought from our old house. I had always called it wild ageratum but have since discovered a much more romantic-sounding name, blue mist flower. Scientific names seem to keep changing these days, but the current name seems to be Conoclinium coelestinum.
The plant grows on roadsides in our area, but I've not been able to get it to spread yet in our yard.
The white-flowering plant next to it was a mystery volunteer in the meadow garden last year, was allowed to go to seed, and is now everywhere.
Good news: our unknown visitor seems to be Eupatorium hyssopifolium, hyssop-leaved thoroughwort, a native that is actually threatened in neighboring Ohio.
I am pleased to report that it seems to be happy here in wild, wonderful West Virginia.