Liatris pycnostachya is commonly cultivated. Collections from Michigan 'doubtless represent escapes' (E. G. Voss, pers. comm.), as also do those from Massachusetts, New Jersey, and New York.
From Flora of Indiana (1940) by Charles C. Deam
A very rare species of prairies. Liatris pycnostachya, which does not occur in Indiana, has been reported from Jasper, Marshall, St. Joseph, and Vigo Counties and Schneck reported it from the Lower Wabash Valley. Doubtless all of these reports should go to this species. A specimen in the herbarium of Purdue University collected in St. Joseph County by Barnes and labeled L. pycnostachya is L. Bebbiana. I have seen the Jasper County specimen and it belongs here. Blatchley reported it from Vigo County. He collected his specimen in the Haeckland Prairie in 1889 and it is now in the herbarium of Butler University. I collected my specimen in the same place in 1917. Since the Lower Wabash Valley has no prairies on the Indiana side of the river where Dr. Schneck collected, it is best to refer his specimen to Illinois.