Non-native Invasive Freshwater Plants

Garden Loosestrife (Lysimachia vulgaris)

General Information

Garden loosestrife Lysimachia vulgaris is an attractive wetland perennial that was apparently introduced to Washington as an ornamental landscaping plant. However, garden loosestrife has the ability to invade and establish itself in wetlands and along lake and river shorelines. Where purple loosestrife and garden loosestrife grow together along Lake Sammamish shorelines, garden loosestrife is far more abundant and appears to outcompete purple loosestrife.

Distribution

Garden loosestrife is a native of Eurasia, where it occurs in fens, wet woods, lakeshores and riverbanks almost throughout Europe. In North America, it is naturalized in parts of Quebec, Illinois, Ohio, Kentucky, West Virginia, and Pennsylvania. In the west, garden loosestrife is found in Colorado, Montana, Oregon, Washington, and British Columbia (PLANTS database). The earliest herbarium collection of garden loosestrife from Washington was made in 1978 from the east-northeast corner of Lake Washington. The most extensive populations in Washington are in King County where garden loosestrife grows along the shorelines of Lake Sammamish and Lake Washington. It has also been reported Chambers Lake in Thurston County, Loon Lake in Stevens County and from Skagit and Whatcom Counties.

Growth Habit

Garden loosestrife grows in moist habitats, such as fens, wet woods, wetlands, riparian areas, and lakeshores, but it may also be found in upland sites. It is a perennial plant that appears to remain in the vegetative stage for some time prior to blooming. The presence of a flowering specimen indicates it has been in an area for some years. Garden loosestrife spreads by seed and vegetatively. King County reports that the rhizomes from a single plant can be up to 15 feet long. Garden loosestrife produces bright yellow clusters of flowers from July to September. Its dense growth habit displaces native wetland vegetation and reduces habitat for fish and wildlife.

Management

The King County Noxious Weed Control Board requires control of garden loosestrife (Class B noxious weed in Washington). They report that small areas of garden loosestrife seedlings can be dug up and larger isolated plants can be removed by hand if care is taken to remove all rhizomes. They do not recommend only pulling this plant because it breaks off easily leaving rhizomes behind to regrow. Garden loosestrife has been covered with black plastic at least one site on Lake Sammamish. This can be effective for controlling seedlings or on very small populations. It can also serve as a suppression tool where herbicides are not desired. King County reports that the aquatic formulations of glyphosate, triclopyr, and imazapyr are effective on garden loosestrife. No biological control agents are presently known and no research to discover biological control agents is currently being conducted.

Identification

Although when not flowering garden loosestrife may be confused with purple loosestrife, it does not have square stems like purple loosestrife. Another loosestrife, yellow loosestrife (Lysimachia punctata) may be confused with garden loosestrife. Yellow loosestrife also has yellow flowers but these flowers occur all along the plant stem and not just at the top of the plant.

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