Purple loosestrife (Lythrum salicaria) is a perennial plant native to Eurasia where it grows along streams, rivers, and wet seepage areas (fig. 1). Seeds were inadvertently brought to North American territories in the ballast water of ships. Purple loosestrife was also intentionally planted throughout North America for its ornamental flowers but has since escaped cultivation to spread to wetlands.

Some purple loosestrife plants release millions of seeds during the summer season, and these seeds readily disperse to new wetlands via water, animals, and even on people’s shoes. In addition, both its roots and stem fragments can sprout and begin new plants.

When purple loosestrife invades a wetland, the species sometimes becomes more dominant than the original native wetland species, such as cattails and sedges. While many people think that purple loosestrife reduces the value of wetlands for wildlife, these claims are disputed. Most people agree, however, that purple loosestrife grows more prolifically in North America than elsewhere, probably because the species has left its native enemies behind in Eurasia and Australia. Although we do not understand how well the species grows in various climates, there is some thought that purple loosetrife may never fully invade the southern United States. Studies looking at the species’ response to temperature and analyses of its growth patterns across latitudes can help us determine its future threat to uninvaded portions of the United States. This is where volunteers come in.

Volunteers in North America, Eurasia, and Australia are helping assess purple loosestrife growth in their regions (fig. 2). The program is part of Dr. Beth Middleton’s project to compare the role of purple loosestrife in its native and invasive habitats. Anyone can participate, and volunteers currently include high school and college students, retirees, professionals from all disciplines, agency personnel, and university faculty. Volunteers collect data by marking off a sampling area, recording the number and height of purple loosestrife, and observing the sunlight and water conditions at each location. Data collection only occurs once in each wetland and takes less than 30 minutes (see form below). The results of the study will help efforts to control and predict the future spread of this species.