Lythrum salicaria L.

Common Name: Purple loosestrife

Synonyms and Other Names:

Purple loosestrife; Spiked loosestrife; Salicaire; Bouquet violet; Rainbow weed

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Identification: Purple loosestrife is an erect perennial herb in the loosestrife family (Lythraceae) that develops a strong taproot, and may have up to 50 stems arising from its base. Its 50 stems are four-angled and glabrous to pubescent. Its leaves are sessile, opposite or whorled, lanceolate (2-10 cm long and 5-15 mm wide), with rounded to cordate bases. Leaf margins are entire. Leaf surfaces are pubescent (USDA Plants Database 2008). Each inflorescence is spike-like (1-4 cm long), and each plant may have numerous inflorescences. The calyx and corolla are fused to form a floral tube (also called a hypanthium) that is cylindrical (4-6 mm long), greenish, and 8-12 nerved. Typically the calyx lobes are narrow and thread-like, six in number, and less than half the length of the petals. The showy corolla (up to 2 cm across) is rose-purple and consists of five to seven petals.  Twelve stamens are typical for each flower. Individual plants may have flowers of three different types classified according to stylar length as short, medium, and long. The short-styled type has long and medium length stamens, the medium type has long and short stamens, and the long-styled has medium to short stamens. The fruit is a capsule about 2 mm in diameter and 3-4 mm long with many small, ovoid dust-like seeds (< 1 mm long) (USDA plants database 2008).

Size: can grow up to 2.5 m tall, forming colonies 1.5 m or more in width

Native Range: Eurasia; extends from Great Britain to central Russia from near the 65th parallel to North Africa; Japan, Korea, Southeast Asia and northern India, and the northern Himalayan region.

Great Lakes Nonindigenous Occurrences: This species was introduced to North America in the early 1800s where it first appeared in ballast heaps of eastern harbors (Stuckey 1980). According to the U.S. Fish and Wildlife Service, purple loosestrife now occurs in every state except Florida. The species has also been introduced to Australia, Tasmania, and New Zealand. The first Great Lakes sighting was in Lake Ontario in 1869.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Lythrum salicaria are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IN190020142Little Calumet-Galien; St. Joseph
MI1839202169Au Gres-Rifle; Au Sable; Bad-Montreal; Betsie-Platte; Betsy-Chocolay; Birch-Willow; Black; Black-Macatawa; Black-Presque Isle; Boardman-Charlevoix; Brule; Carp-Pine; Cass; Cedar-Ford; Cheboygan; Clinton; Dead-Kelsey; Detroit; Escanaba; Fishdam-Sturgeon; Flint; Great Lakes Region; Huron; Kalamazoo; Kawkawlin-Pine; Keweenaw Peninsula; Lake Erie; Lake Huron; Lake Michigan; Lake St. Clair; Lake Superior; Little Calumet-Galien; Lone Lake-Ocqueoc; Lower Grand; Manistee; Manistique River; Maple; Menominee; Michigamme; Millecoquins Lake-Brevoort River; Muskegon; Northeastern Lake Michigan; Northwestern Lake Huron; Northwestern Lake Michigan; Ontonagon; Ottawa-Stony; Pere Marquette-White; Pigeon-Wiscoggin; Pine; Raisin; Saginaw; Shiawassee; Southeastern Lake Michigan; Southwestern Lake Huron; St. Clair; St. Clair-Detroit; St. Joseph; St. Joseph; St. Marys; Sturgeon; Tacoosh-Whitefish; Tahquamenon; Thornapple; Thunder Bay; Tiffin; Tittabawassee; Upper Grand; Waiska; Western Lake Erie
MN198720186Baptism-Brule; Beartrap-Nemadji; Beaver-Lester; Cloquet; Lake Superior; St. Louis
NY1869201715Buffalo-Eighteenmile; Cattaraugus; Chaumont-Perch; Irondequoit-Ninemile; Lake Ontario; Lower Genesee; Mettawee River; Niagara River; Oak Orchard-Twelvemile; Oneida; Oswego; Salmon-Sandy; Saranac River; Seneca; St. Lawrence
OH1902202213Ashtabula-Chagrin; Auglaize; Black-Rocky; Blanchard; Cedar-Portage; Cuyahoga; Grand; Huron-Vermilion; Lake Erie; Lower Maumee; Sandusky; Southern Lake Erie; Western Lake Erie
PA200820212Chautauqua-Conneaut; Lake Erie
VT189820192Lake Champlain; Otter Creek
WI1928201824Bad-Montreal; Beartrap-Nemadji; Black-Presque Isle; Brule; Door-Kewaunee; Duck-Pensaukee; Fox; Lake Michigan; Lake Superior; Lake Winnebago; Lower Fox; Manitowoc-Sheboygan; Menominee; Milwaukee; Northwestern Lake Michigan; Northwestern Lake Michigan; Oconto; Ontonagon; Peshtigo; Pike-Root; Southwestern Lake Superior; St. Louis; Upper Fox; Wolf

Table last updated 5/25/2024

† Populations may not be currently present.

Ecology: Purple loosestrife is a wetland plant, growing in freshwater wet meadows, tidal and non-tidal marshes, river and stream banks, pond edges, reservoirs, and ditches. It prefers moist, highly organic soils but can tolerate a wide range of conditions. It grows on calcareous to acidic soils, can withstand shallow flooding, and tolerates up to 50% shade. Purple loosestrife has low nutrient requirements and can withstand nutrient-poor sites. It flowers from July until September or October. Flowering occurs 8-10 weeks after initial spring growth. Thompson et al. (1987) estimated that on average, a mature plant produces about 2,700,000 seeds annually. Seeds are relatively long-lived, retaining 80% viability after 2-3 years of submergence (Malecki 1990). 

Means of Introduction: Purple loosestrife seeds are mostly dispersed by water, but wind and mud adhering to wildlife, livestock, vehicle tires, boats, and people serve also as agent. It was introduced into North America through ship ballast and as an ornamental. In states where it is permitted, purple loosestrife continues to be promoted by horticulturists for its beauty as a landscape plant and for bee-forage. It was probably introduced to the Great Lakes region via canals.

Status: Established. At the state level, it has been classified as noxious and has a highly invasive status and wetland indicator values. L. salicaria has been labeled the “purple plague." because of its epidemic devastation to natural communities. The species is included on the Nature Conservancy’s list of “America’s Least Wanted -- The Dirty Dozen” (Flack & Furlow 1996). In response to the alarming spread of this exotic species, at least 13 states (including Minnesota, Illinois, Indiana, Ohio, Washington, and Wisconsin) have passed legislation restricting or prohibiting its importation and distribution (Malecki et al. 1993; Strefeler et al. 1996b). 

Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...


Lythrum salicaria has a high environmental impact in areas where it has become established and is not controlled.

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 cover, food, or nesting sites for native wetland animals (U.S.EPA 2008). 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.

Specialized marsh birds avoid nesting and foraging in purple loosestrife (Blossey et al. 2001). The federally endangered bog turtle (Clemmys muhlenbergi Schoepff) loses basking and breeding sites to encroachment of purple loosestrife (Malecki et al. 1993). While some avian fauna, such as the swamp sparrow (Melospiza georgiana), have successfully utilized purple-loosestrife dominated habitat around Lake Huron, overall avian diversity in these sites is much lower compared to other wetland habitats (Whitt et al. 1999). Additionally, species richness in wetland moth populations has been shown to be negatively correlated with purple loosestrife cover (Schooler et al. 2009).

Numerous studies demonstrate the aggressive and competitive nature of purple loosestrife. Fernald (1940) reported a loss of native plant diversity in the St. Lawrence River floodplain following the invasion of purple loosestrife and the exotic flowering rush, Butomus umbellatus. Purple loosestrife was determined to be the most common exotic species of the St. Lawrence River wetlands, appearing at more survey stations than any nonindigenous plant (although not at the highest densities) (Lui et al. 2005). However, L. salicaria appeared to have a lesser effect on plant diversity at colonized sites relative to grass exotics, reed canary grass (Phalaris arundinacea) and common read (Phragmites australis) (Lui et al. 2005).  Surveys of coastal wetlands on the Great Lakes found L. salicaria to be the one of the most common emergent exotic plants across the Lakes and indicated that L. salicaria presence was associated with a significant reduction in species richness (Trebitz and Taylor 2007). Gaudet and Keddy (1988) report declining biomass for 44 native wetland species in a laboratory setting with the establishment of L. salicaria.  Among twenty tested wetland plants, (Keddy et al. 1994) found purple loosestrife to be among the most competitive, causing an average yield reduction of 60% in its neighbors across different habitats. Keddy et al. (1998) also found that competition with L. salicaria could reduced the above-ground biomass of adjacent target species by over 80%, more than 6 other tested competitors, including T. augustifolia. However, despite growth reduction, target species survival was also highest in L. salicaria pots (Keddy et al. 1998). In the Hamilton Marshes adjacent to the Delaware River, annual above-ground production of L. salicaria far exceeded all other plant species’ production combined.

Purple loosestrife causes annual wetland losses of about 190,000 hectares in the United States (Thompson et al. 1987; Mal et al. 1997). At the Effigy Mounds National Monument (EFMO), combined populations of purple loosestrife cover an area of 5 to 10 hectares growing in regularly disturbed sites.  This species has a major visual impact on the vegetation of EFMO, and it has the potential to invade and replace native communities endangering the areas' primary resources (Butterfield et al. 1996).   

The invasion of L. salicaria alters biogeochemical and hydrological processes in wetlands. Areas dominated by purple loosestrife (Fig. 2) show significantly lower porewater pools of phosphate in the summer compared to areas dominated by Typha latifolia L. (Templer et al. 1998).

Purple loosestrife leaves decompose quickly in the fall resulting in a nutrient flush, whereas leaves of native species decompose in the spring (Barlocher and Biddiscombe 1996; Emery and Perry 1996; Grout et al. 1997). This change in timing of nutrient release at a time of little primary production results in significant alterations of wetland function and could jeopardize detritivore consumer communities adapted to decomposition of plant tissues in spring (Grout et al. 1997).

Current research on the socio-economic impact of Lythrum salicaria in the Great Lakes is inadequate to support proper assessment.

Since the 1980s, purple loosestrife has received an increasing amount of attention from the media nationally, almost always in a negative light (Lavoie, 2010). However, no quantitative studies are known to have measured the societal perception of purple loosestrife. Because of its ability form dense homogeneous stands and reduce waterfowl habitat, it is perceived as a species which is dominating and inhibitive to duck hunting.

Current research on the benefits of Lythrum salicaria in the Great Lakes is inadequate to support proper assessment.

Although sale, purchase, and distribution of purple loosestrife is illegal in all Great Lakes states, a positive perception of purple loosestrife as a gardening/ornamental species butterflies is still represented in some media sources due to its beauty and ability to attract bees and other pollinators (Lavoie 2010).

Management: Regulations (pertaining to the Great Lakes)

Now regulated in all Great Lakes states. Lythrum salicaria is listed as an exotic weed in Illinois (525 ILCS 10/3, 10/4) making it illegal to buy, sell or distribute plants, its seeds, or any part without a permit.  Planting, sale, or other distribution without a permit is also prohibited in Indiana (312 IAC 14-24-12).  Purple loosestrife – including all cultivars – is a prohibited invasive species in Minnesota (MN Administrative Rules, 6216.0250 Prohibited). The species is restricted in Michigan, with an exemption for sterile cultivars (MI NREPA 451, Section 324.41301). Planting or sale of the species without a permit is prohibited in Ohio (O.R.C. ' 927.682), though the director may exempt varieties ‘demonstrated not to be a threat to the environment’.  Pennsylvania has designated all nonnative Lythrum species and their cultivars as noxious weeds (7 PA Code 110.1). Purple loosestrife is designated both as a restricted species (NR40.05: Restricted) and as an invasive aquatic plant (NR 109.07 (2)) in Wisconsin


Biological control agents do not eliminate the target weed, but when successful, can sup- press weed populations to a nonsignificant level (Rees et al. 1996). Five species of beetles have been approved for the biocontrol of Lythrum salicaria (Blossey et al 1994ab). 
Galerucella calmariensis and G. pusilla are both leaf-feeding chrysomelids. These beetles defoliate and attack the terminal bud area, drastically reducing seed production. The mortality rate to purple loosestrife seedlings is high. Evidence of Galerucella ssp. damage are round holes in the leaves. Four to six eggs are laid on the stems, axils or leaf underside. The larvae feed constantly on the leaf underside, leaving only the thin cuticle layer on the top of the leaf.  Initial introductions in eastern North America occurred in Virginia, Maryland, Pennsylvania, New York, Minnesota, and southern Ontario in August, 1992 (Hight et al., 1995).  In 1992 these three beetles were released in Washington.  By 1996 populations of Galerucella ssp. visibly impacted purple loosestrife stands ( 2012).  In the Great Lakes region, Sea Grant conducted an extensive, multi-state program involving youth in raising and releasing Galerucella beetles for control of purple loosestrife (Sea Grant 2001).

Hylobius transversovittatus is a root-mining weevil that also eats leaves. This beetle eats from the leaf margins, working inward. The female crawls to the lower 2-3 inches of the stem then bores a hole to the pithy area of the stem where 1 -3 eggs are laid daily from July to September. Or, the female will dig through the soil to the root, and lay eggs in the soil near the root. The larvae then work their way to the root. H. transversovittatus damage is done when xylem and phloem tissue are severed, and the carbohydrate reserves in the root are depleted. Plant size is greatly reduced because of these depleted energy reserves in the root. The larvae evidence is the zig-zag patterns in the root. 
Nanophyes marmoratus and N. brevis are seed eating beetles. Young adults feed on new leaves on shoot tips, later feeding on the flowers and closed flower buds. Sixty to one hundred eggs are laid in the immature flower bud. Seed production is reduced by 60%. There were two test sites releases in 1996.  Approval to introduce N. marmoratus was granted followed by introductions in New York and Minnesota in 1994. Additional releases occurred in New Jersey in 1996. N. marmoratus has also been released in Ohio (Ohio EPA 2001).  Release of N. brevis planned for 1994 was delayed due to contamination of the original shipment with a parasitic nematode (Piper, 1997).  This infection appeared benign for N. brevis, however, due to the potential for non-target effects of the nematode after introduction into North America, only disease free specimens should be introduced, which, at present, effectively precludes the introduction of N. brevis (Blossey 2002).

Bayeriola salicariae, a gall midge, was studied and screened between 1990 and 1992 (Blossey and Schroeder, 1992).  Based on results indicating a potential wider host range, the gall midge B. salicariae was not proposed for introduction (Blossey and Schroeder, 1995).

Targeted grazing by sheep has also been used as a biocontrol (Kleppel and LaBarge 2011).

Revegetation of disturbed riparian sites can be used to prevent purple loosestrife establishment and to reduce re-establishment after control procedures are applied.  Fowl mannagrass (Glyceria striata), foxtail sedge (Carex alopecoidea), and reed canarygrass (Phalaris arundinacea) have achieved dominance and prevented re-invasion in plots where purple loosestrife was experimentally removed. Smartweed (Polygonum lapathifolium) is reported to out-compete purple loosestrife during its first year of growth.  Seeding Japanese millet (Echinocloa frumentacea, also called billion-dollar grass) at 30 pounds/acre on exposed moist soil after drawdown and before purple loosestrife seedlings began to grow provided control. Japanese millet is considered an exceptional wildlife plant (Jacobs 2008).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Most mechanical and cultural attempts to control purple loosestrife are ineffective. A single known exception is cutting followed by flooding.

For small infestations and isolated plants, hand pulling may be effective.  Pull individual loosestrife plants by hand before seed is set . The entire root system must be removed, but do not dig out roots because soil disturbance may release seeds buried in the soil and break off plant parts, which then reproduce.  Instead, a cultivator may be used to tease roots from the soil.  All plant parts should be bagged to prevent dispersal or resprouting and preferably burned.  Follow-up treatments are recommended for at least 3 years.

Frequent cutting of the stems at ground level is effective but must be continued for several years. (Courtney 1997).  Mowing is generally not effective as it exposes the seed bank. 

Flooding is generally ineffective at controlling purple loosestrife, though some success has been reported for control of seedlings when using flooding regimes in excess 30cm for over 7 weeks (Balogh 1985). 

Prescribed burning is not an effective management tool for purple loosestrife.  The dead upright stems do not carry fire well and the fine fuels are often lacking. The growing points of the root crown are about 2 cm (0.8 inch) below the soil surface, so surface fires are not likely to inflict much damage. Purple loosestrife begins spring growth about a week or 10 days after broadleaved cattails, so a fire of sufficient intensity to damage purple loosestrife could also damage desirable native species (IL DNR 2007).

Only herbicides permitted for wetland use may be used to control purple loosestrife.  There are four chemicals that can be used to manage purple loosestrife on sites with standing or moving water typical of where it invades. Triclopyr and glyphosate are used most commonly. However, 2,4-D, and imazapyr are also formulated for aquatic applications.  Widespread elimination of standing biomass may result in the exposure and sprouting of the immense purple loosestrife seed bank. Thus broadleaf-specific herbicides which do not harm monocot species (such as common wetland grasses and sedges) are preferred. The most species specific way to apply herbicide is by cutting and treating the stems. Foliar spray can be used by applying herbicide after the period of peak bloom, in late August. Any control method should be followed up on a yearly basis to catch any missed plants or new sprouts. (Ohio EPA 2001)

See also:

Midwest Invasive Plant Network - Invasive Plant Control Database

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: Other species of Lythrum that grow in the United States have 1-2 flowers in each leaf-like inflorescence bract and eight or fewer stamens compared to L. salicaria, which has more than two flowers per bract and typically twelve stamens per flower. L. virgatum, another species introduced from Europe closely resembles L. salicaria, but differs in being glabrous (lacking plant hairs), and having narrow leaf bases. The latter two species interbreed freely producing fertile offspring, and some taxonomists (Rendall 1989) consider them to be a single species. 

Four species have been approved for introduction for biocontrol of purple loosestrife and have been released: a root-mining weevil, Hylobius transversovittatus Goeze; two leaf beetles, Galerucella calmariensis L. and Galerucella pusilla Duftschmidt; and a flower-feeding weevil, Nanophyes marmoratus Goeze.

References (click for full reference list)

Other Resources:
USGS/NAS Technical Species Profile

Cornell University Non-indigenous Plant Species Program, 


Jil M. Swearingen, National Park Service, Washington, DC. 

Plant Materials   Plant Fact Sheet/Guide Coordination Page   National Plant Data Center

USGS - Wetland Plants and Plant Communities of Minnesota and Wisconsin


Virginia Natural Heritage Program,

Author: Cao, L., J. Larson, and R. Sturtevant

Contributing Agencies:

Revision Date: 7/28/2022

Citation for this information:
Cao, L., J. Larson, and R. Sturtevant, 2024, Lythrum salicaria L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 7/28/2022, Access Date: 5/25/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.