Purple Loosestrife
Lythrum salicaria L.

SOURCE: The following information on this species is taken, in part, from the Plant Conservation Alliance, Alien Plant Working Group, Weeds Gone Wild website, Fact Sheets. The Fact Sheet information for this species can be found at http://www.nps.gov/plants/alien/factmain.htm. Modifications include additional pictures (from www.invasives.org) and resource information. Specific species management and control information is provided elsewhere. Check the website link provided to check for future updates. The last update for this fact sheet is March, 2005.

NATIVE RANGE: Eurasia; throughout Great Britain, and across central and southern Europe to central Russia, Japan, Manchuria China, southeast Asia and northern India

DESCRIPTION: Purple loosestrife is an erect perennial herb in the loosestrife family, with a square, woody stem and opposite or whorled leaves. Leaves are lance-shaped, stalkless, and heart-shaped or rounded at the base. Plants are usually covered by a downy pubescence.

Photo: Linda Wilson, University of Idaho, www.forestryimages.org

Loosestrife plants grow from four to ten feet high, depending upon conditions, and produce a showy display of magenta-colored flower spikes throughout much of the summer. Flowers have five to seven petals. Mature plants can have from 30 to 50 stems arising from a single rootstock.

Photo: Linda Wilson, Univ. of Idaho, www.forestryimages.org.

Photo: Illinois Vegetation Management Guidelines, http://www.inhs.uiuc.edu/chf/outreach/VMG/VMG.html

ECOLOGICAL THREAT: Purple loosestrife adapts readily to natural and disturbed wetlands. As it establishes and expands, it outcompetes and replaces native grasses, sedges, and other flowering plants that provide a higher quality source of nutrition for wildlife. The highly invasive nature of purple loosestrife allows it to form dense, homogeneous stands that restrict native wetland plant species, including some federally endangered orchids, and reduce habitat for waterfowl.

Photo: Agriculture and Agri-Food Canada Archives, Agriculture and Agri-Food Canada, www.forestryimages.org.

DISTRIBUTION IN THE UNITED STATES: According to the U.S. Fish and Wildlife Service, purple loosestrife now occurs in every state except Florida.

HABITAT IN THE UNITED STATES: Purple loosestrife is capable of invading many wetland types, including freshwater wet meadows, tidal and non-tidal marshes, river and stream banks, pond edges, reservoirs, and ditches.

BACKGROUND: Purple loosestrife was introduced to the northeastern U.S. and Canada in the 1800s, for ornamental and medicinal uses. It is still widely sold as an ornamental, except in states such as Minnesota, Wisconsin, and Illinois where regulations now prohibit its sale, purchase and distribution.

BIOLOGY & SPREAD: Purple loosestrife enjoys an extended flowering season, generally from June to September, which allows it to produce vast quantities of seed. The flowers require pollination by insects, for which it supplies an abundant source of nectar. A mature plant may have as many as thirty flowering stems capable of producing an estimated two to three million, minute seeds per year.

Purple loosestrife also readily reproduces vegetatively through underground stems at a rate of about one foot per year. Many new stems may emerge vegetatively from a single rootstock of the previous year. "Guaranteed sterile" cultivars of purple loosestrife are actually highly fertile and able to cross freely with purple loosestrife and with other native Lythrum species. Therefore, outside of its native range, purple loosestrife of any form should be avoided.

SUGGESTED ALTERNATIVE PLANTS: Native species of Liatris (blazing star) have showy pink-purple flower spikes and are an important nectar source for many native species of butterflies and other insects.

AUTHOR:
Jil M. Swearingen, U.S. National Park Service, Washington, DC.

For more information on garlic mustard, please contact:
Cornell University Non-indigenous Plant Species Program http://www.invasiveplants.net
Delaware River Invasive Plant Partnership, http://www.paflora.org/DRIPP.html
Illinois Vegetation Management Guidelines, http://www.inhs.uiuc.edu/chf/outreach/VMG/VMG.html
Invasive Plant Atlas of New England, http://invasives.eeb.uconn.edu/ipane/
Ohio Department of Natural Resources, Fact Sheets, http://www.dnr.state.oh.us/dnap/invasive/4loosestrife.htm
Southeast Exotic Pest Plant Council, Invasive Plant Manual, http://www.se-eppc.org/manual/
The Bugwood Network, http://www.invasive.org/
The Nature Conservancy Invasive Species Initiative, http://tncweeds.ucdavis.edu/esadocs.html
Virginia Natural Heritage Program http://www.state.va.us/~dcr/dnh/invlyth.htm
Virginia Tech Weed Identification Guide, http://www.ppws.vt.edu/weedindex.htm

REFERENCES:
Heidorn, R. and B. Anderson. 1991. Vegetation management guideline: purple loosestrife (Lythrum salicaria L.). Natural Areas Journal 11:172-173.
LaFleur, A. 1996. Invasive plant information sheet: purple loosestrife. The Nature Conservancy, Connecticut Chapter.
Malecki, R.A. (et al.). 1993. Biological control of purple loosestrife (Lythrum salicaria). BioScience 43 (10):680-686.
The Nature Conservancy. Purple Loosestrife: Element Stewardship Abstract. In: Wildland Weeds Management & Research Program, Weeds on the Web.
Thompson, Daniel Q., Ronald L. Stuckey, Edith B. Thompson. 1987. Spread, Impact, and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands. U.S. Fish and Wildlife Service. 55 pages.
Virginia Department of Conservation and Natural Resources. 1995. Invasive Alien Plant Species of Virginia: Purple Loosestrife (Lythrum salicaria).

Plant Conservation Alliance, Alien Plant Working Group.

Management and Control Information

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