It has the ability to invade natural wetlands and displace native plants such as cattails and sedges. It also affects agriculture by becoming a nuisance in moist rangelands and in crops planted in flood plains. Unfortunately, Lythrum salicaria cannot be distinguished from the non-agressive Lythrum virgatum and many states broadened their regulations to include all cultivars and nonnative species of Lythrum so that their previous restrictions on purple loosestrife could be enforced. Nurserymen and commercial growers have protested these regulations claiming that several of their cultivars were sterile, and that the broad ban on loosestrife would hurt their businesses. Some gardeners supported the nurserymen's viewpoint saying that they have never seen any seedling development, but other gardeners have had different experiences.
Purple loosestrife has a specialized method of reproduction.
Purple loosestrife has three types of flowers, with only one type of flower per individual plant. These trimorphic flowers each differ by having pistils of varying lengths. Each type of flower also has two different whorls of stamens that vary in length, but are never the same length as the pistil or each other. These can be observed easily without magnification. Neil O. Anderson and Peter D. Ascher in the Department of Horticultural Science at the University of Minnesota, have conducted thorough investigations on the fertility of purple loosestrife and several of the cultivars of Lythrum.