Purple Loosestrife (Lythrum salicaria)

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Purple loosestrife is a herbaceous wetland perennial. Purple loosestrife has square, woody stalks growing to a height of 1-2 meters. It has smooth edged leaves which are 5-10 cm in length, attached directly to the stalk opposing one another (or occasionally, alternate). Plants are usually covered by a downy pubescence. The plant forms 10-40 cm long pink/purple flowering spikes. Flowers have five to seven petals. Mature plants can have from 30 to 50 stems arising from a single rootstock.

Key Identifiers
  • Purple loosestrife has a long purple flower stalk and can grow to 2 m in height.
  • Purple loosestrife flowers have 5-7 bright purple, wrinkled petals. Purple loosestrife has a square woody stem and opposite leaves.
Location in Canada
Purple loosestrife is found in southern provinces from BC to Newfoundland. The first "official" report of Purple Loosestrife in Alberta was recorded in September 1990 at Medicine Hat. Since that time, the Province has made great efforts to control purple loosestrife with encouraging success.

Gayah Sieusahai, ARD
Resources Similar species
Fireweed (Epilobium angustifolium) is often mistaken for Purple Loosestrife but has a round stem and long seed pods at the base of the flower spike.

Liatris sp is a garden plant that is sometimes confused with Purple loosestrife however it has very dense flower clusters and thin string-like petals.

Other Documents in the Series

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Pale Yellow Iris (Iris pseudacorus)
Purple Loosestrife (Lythrum salicaria) - Current Document
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For more information about the content of this document, contact Chris Neeser.
This document is maintained by Shelley Barkley.
This information published to the web on April 10, 2012.
Last Reviewed/Revised on August 21, 2018.