I think you are right that it may have been introduced. I have never seen this plant anywhere except on my property. It is attractive enough that some previous resident may have planted it here. It originally grew only in one fence line, however, where there was unlikely to have ever been a flower bed; since then it has spread to unmown areas near that spot, spreading by seeds falling under each plant.
I think I will take specimens to some good local nurseries to see whether anyone recognizes it.
