Hmmm. Check monkshood or wolf's bane at http://www.blossomfarm.com/plants_ac-an.htm or harebell at http://www.prairiefrontier.com/pages/natvpics/nativea4.html Since you used wildflower seeds, I think that harebell (a species of campanula) might be the plant. Only, it's not exactly purple. Monkshood is much darker, but ... Have you noticed itching after handling the plant? Monkshood is poisonous.

-- erlik