Tardivo is the king of radicchio.  Heads of it resemble curly purple witch fingers.  It is expensive and nearly impossible to find in America.  But if you chance upon it, don’t be intimidated by its vaguely pernicious looks. Generally when you buy radicchio in America it is a slightly browned ball (which we call Radicchio Rosso or Radicchio di Verona in Italy) that has inexpertly traveled from the Veneto (or the Salinas Valley) to your local supermarket.