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Purple Loosestrife

Closeup of Purple Loosestrife Flowers; Photo credit:Anne Elliott, http://www.flickr.com/photos/71833159@N00/Purple loosestrife plan in bloom; Photo credit:  Bob Osborn, Yeovil, England,  www.wbdpublications.co.ukPurple loosestrife flower spike; photo credit:  Ohio State Weed Lab Archive, The Ohio State University, Bugwood.orgPurple Loosestrife stem, photo credit: Amber Burch Purple loosestrife  young plant; Photo Credit: Brian Ostwald

(Lythrum salicaria and L. virgatum)

Common Names

purple lythrum, bouquet-viole, spiked loosestrife

Description

Purple loosestrife is a perennial that can grow up to ten feet in height and typically prefers moist or riparian habitat. Due to the numerous four-sided stems that are green to purple in appearance, this plant appears woody and bush-like in appearance. Clasping leaves have smooth margins, are lance shaped,  and are heart-shaped or rounded at the base. Purple loosestrife leaves and stems are covered by downy fine hairs, and leaves are whorled or alternate on the stem. In autumn with dehydration, the leaves of purple loosestrife turn red in color. The showy purple to magenta colored flowers are clustered on a long spike that can extend two inches to three feet down the stem called a raceme. Each flower has five to seven petals and blooms from June to September. Seeds burst at maturity around late July or early August, with each stem producing up to three million tiny seeds per year. Purple loosestrife has a dense, woody, and extensive root system. This root system and the prolific seed production results in rapid spread of loosestrife. In addition, stems of the plant that are broken off or disturbed often grow shoots.

Key Features

The square or octagonal stems, the red leaves if the plant gets dried out in the fall, and the long clusters of showy purple to rose colored flowers.

Habitat

As a general rule, moisture is required for growth and reproduction, however, well-established plants can persist on dry sites.  It is well suited to seasonal wetlands, and is capable of invading wet meadows, river and stream banks, pond edges, reservoirs, and ditches, irrigation canals, and marshes.

Currently found in the following counties:

Big Horn, Carbon, Cascade, Chouteau, Custer, Hill, Lake, Lewis & Clark, Liberty, Meagher, Missoula, Park, Ravalli, Rosebud, Sheridan, Valley, Wheatland

IWM

Interesting Facts

In the past, purple loosestrife was used as a medicinal herb for treatment of diarrhea, dysentery, bleeding, wounds, ulcers and sores. It is an herb that was introduced as a garden perennial from Europe during the 1800's, and unfortunately, today it is still widely sold as an ornamental.

Commonly Confused Plants

  • Blazing star
  • fireweed
  • spirea

Alternative Plants

  • Spiked Speedwell (Veronica spicata)
  • Spiked Gayfeather, Blazing Star (Liatris spicata)
  • Garden Sage (Salvia)
  • Purple Coneflowe (Echinacea purpurea)

Visit our library for additional articles on purple loosestrife.

Photo Credits: Anne Elliott, http://www.flickr.com/photos/71833159@N00/; Bob Osborn, Yeovil, England,  www.wbdpublications.co.uk; Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org; Amber Burch; Brian Ostwald

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