Purple loosestrife flower headHundreds of vibrant magenta or purple flowers standing three to seven feet tall over Apostle Islands wetlands may look pretty, but dig a little deeper into the story of purple loosestrife (Lythrum salicaria) and you'll understand why this invasive plant poses an ongoing threat. A single plant can produce a million seeds or more. And left to multiply, these highly aggressive plants from Asia and Europe can choke out native vegetation, leaving wildlife without proper food, nesting grounds, or shelter. The plants flower from July into the fall. Removing the flower...