Eupatorium coelestinum, wild ageratum, blue mistflower
If you live in western Kentucky, you'll see these purple/blue wildflowers blooming in the road ditches right now.
They are Eupatorium coelestinum, or blue mistflower, also called wild ageratum. They are one of my favorite wildflowers. As you might guess when you look at the flower, they're a member of the aster family.
They like moist areas. I sometimes see them growing side-by-side with goldenrod which is a very nice color combination. This solitary specimen is growing in a damp area in the ditch just up the hill from our mailbox.
Only slightly related:
I couldn't resist buying the flowered handkerchiefs below. They are just a sample of the patterns in the stack of ladies' hankies at the Mennonite store at Fairview (KY.)