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Purple Loosestrife (Lythrum salicaria)    

Purple Loosestrife flower.
Purple Loosestrife flower.

Purple Loosestrife is a semi-aquatic herbaceous plant belonging to the loosestrife family, Lythraceae, native to the wetlands of Eurasia.

It is a herbaceous perennial plant, growing 1-2 m tall, forming clonal colonies 1.5 m or more in width with numerous erect stems growing from a single woody root mass. The stems are reddish-purple and square in cross-section. The leaves are lanceolate, 3-10 cm long and 1-2 cm broad, downy and sessile, and arranged opposite or in whorls of three. The flowers are reddish purple, 10-15 mm diameter, with six petals (occasionally five), and are clustered tightly in the axils of bracts or leaves. The fruit is a small 3-4 mm capsule containing numerous minute seeds. Flowering lasts throughout the summer. When the seeds are mature, the leaves often turn bright red through dehydration in early autumn; the red colour may last for almost two weeks. The dead stalks from previous growing seasons are brown.

Purple loosestrife has become an invasive species since its introduction into temperate New Zealand and North America where it is now considered a noxious weed. The seeds probably first arrived in the plant's non-native areas in muddy ballast water emptied from ships. It has also been used as a medicinal herb and cultivated as a garden plant. The flowers are quite showy and bright, and monotypic fields of purple loosestrife are deceptively attractive. The truth is that purple loosestrife has had a very destructive impact on North American wetland ecology since the early 19th century.

The plants grow vigorously and spread very fast when removed from their natural controlling agents. Infestations result in dramatic disruption in water flow in rivers and canals, and a sharp decline in biological diversity. (From Wikipedia)

Bryan Dallolio and Roger Batt stand in an infestation of Perennial Pepperweed.
Purple Loosestrife rosettes.
Photo Courtesy of Canyon County Noxious Weed Control

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