The major difference involves the lack of the plant's natural enemies. When purple loosestrife arrived in North America during the early 1800's no natural enemies accompanied it. This, along with the plant's abitily to grow in a variety of soil types and in various depths of water, has given purple loosestrife a competitive edge over North America's native wetland plants. Purple loosestrife typically infests areas where native wetland plant communities have been disturbed. This includes manmade disturbances such as digging or moving wetland soils with tractors and bulldozers as well as natural disturbances like droughts and floods.
Purple loosestrife spreads primarily by seed germination in moist soil areas.
A typical 3 year old plant can produce in excess of 1 million seeds. The impact of this weed on North American wetlands has been disastrous. Native wetland plants have been crowded out by purple loosestrife. This in turn causes a reduction in suitable habitat for wildlife, particularly waterfowl and waterbirds like this Green Heron, and reduced productivity for those species which depend on aquatic ecosystems. For example, platform nesting species can not use the stiff stems for nest construction, nor are stems or rootstocks palatable to muskrats.