Purple Loosestrife (Lythrum salicaria)
WEED ALERT

Purple loosestrife is an aggressive, herbaceous semi-aquatic perennial plant native to Europe. Originally introduced to North America in the 1800's as an ornamental, purple loosestrife has now naturalized and spread across Canada and the northern US. This invasive plant is found in shallow wetlands where it aggressively degrades and crowds out the natural vegetation required by wildlife. It is common in southwest BC, particularly on Vancouver Island and the lower Fraser Valley and is found frequently in the Okanagan. Smaller infestations are known from the Kootenays and most recently, from the Quesnel area.

Biology

Purple loosestrife is a hardy, upright perennial that grows to 2 metres. Stems are 4-sided (square), and woody with several stalks per plant. Leaves are long and linear with smooth edges that attach directly to the stem on opposite sides. The numerous flowers with 5-6 petals, are pink-purple in colour and develop from June to September on the terminal spike of each stem.

Reproduction

Reproduction is both by seed and root fragments. Each plant is capable of production up to 2.5 million seeds. Seeds are small and are readily dispersed by moving water, wind, waterfowl, other wildlife and humans. Seeds remain dormant over winter and germinate the following spring or early summer. Seeds may lay dormant for many years before sprouting. Purple loosestrife can also reproduce from root fragments or pieces that may sprout new plants.

Habitat 

Purple loosestrife invades wetlands. Lake and river shores, ditchbanks, marshlands, freshwater tidal flats, and riparian meadows are the predominent areas where puple loosestrife will invade and establish. In some locations purple loosestrife has also begun invading drier sites such as pastures and cropland.

Concern 

Purple loosestrife invades wetland areas where it is able to outcompete most native wetland plant species. As a purple loosestrife infestation increases, the size and diversity of the native plant population decreases, often threatening scarce or rare plants. As purple loosestrife dominates an area, the natural foods and protective cover required for wildlife survival is lost. This may result in the loss of wildlife species or displacement from their natural habitat.

Purple loosestrife - square stem
	Purple loosestrife - seedheads

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