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Purple Loosestrife
  • Introduced from Eurasia, possibly as seeds in ship ballast water

  • Up to 3 metres tall

  • One known site in the Boundary appears to be erradicated

Purple Loosestrife in a Wetland

Purple loosestrife
(Lythrum salicaria)

Quick Identification

  • Four-sided, branching stalk

  • Opposite or sometimes whorled, stalkless leaves with smooth edges

  • Flowers are deep pink to purple and form a spike-like cluster

Most birds will not nest in loosestrife.  Wetlands can lose 50-100% of their native plants when loosestrife invades.  This reduces the food supply of native species causing a reduction in diversity.  Large infestations can block water flow in narrow channels, effecting can effect fish movement.

Prevention is very important with this plant.  We have the opportunity to eradicate this species from the Boundary.  This plant is designated as provincially noxious.  Do not share seeds with friends.  Report it if you see this plant.  It is sometimes confused with native fireweed so learning to identify invasive plants is important to save time.

Flowers are deep pink to purple and bloom mid-June to mid-October. Flower grow clustered along the stem forming a spike. Each flower typically has six petals.

Leaves & Stems
Leave are attached directly to the stem in pairs. The stem is four-sided and branches repeatedly. Many shoots can grow from the same root system.

Purple Loosestrife Infestation

Reproduction & Dispersal
Plant spread by seed, from new shoots from the root system, and from broken pieces of root. Seed spread by wind, water, animals, and human activity.


One plant can produce as many as 2 million seeds in a growing season. Seeds can remain dormant in the soil for many years.

A woody taproot and fibrous, branching root system can support many stalks.

Preferred Habitat
Purple loosestrife grown in wetlands, shallow ponds, and creek and river banks.

Interesting Facts
Introduced as a garden ornamental.

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