This flower (or weed) didn’t escape from gardens but most likely came as a stow-away from Europe and Asia in hay or alfalfa seed in the late 1890’s. Since then it has spread to 45 of the 50 states and has rapidly invaded Wisconsin’s prairies and barrens, as well as pastures, hay fields, ditches and other grassland areas.
Well it might look like a pretty purple flower, the spotted knapweed makes and then secretes chemicals into the soil which kill surrounding plants to aid its evasion.
Spotted Knapweed
Looks can be deceiving.