Lythrum salicaria Purple Loosestrife Lythrum salicaria Purple loosestrife was introduced to America as a garden plant. It has escaped from gardens and become a noxious weed in wetlands. These pests and diseases, however, have not come along to America, so here it can grow in vast numbers, threatening native plant populations.
Some people still grow purple loosestrife in their gardens.
Even the garden varieties that are claimed to be sterile are a problem. They may not make seed on their own, but they pollinate each other. More on purple loosestrife from the Plant Conservation Alliance.