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Purple Loosestrife


Common Name
Purple Loosestrife, Rainbow Weed, Spiked Loosestrife
 
Scientific Name
Lythrum salicaria (Linnaeus 1753)
 

 
Description
  • herbaceous perennial
  • height varies with condition, but generally 1.2-3m
  • stem: woody; four-sided with whorled leaves, square in cross-section; colour reddish-purple 
  • leaves: 3-10cm long and 5-15mm broad; lance-shaped but heart-shaped or rounded at the base; arranged in whorls of 3
  • flowers: magenta-colored; trimorphic; 5-7 petals (usually 6); 12 stamens
  • fruit: small 3-4mm capsules with numerous tiny seeds
  • reproduces by producing seeds and vegetative (clonal) propagation
  • sometimes confused with fireweed (Epilobium angustifolium)
 
Habitat
Purple loosestrife prefers moist soil and is therefore capable of invading a wide variety of wetland habitats such as marshes, stream and river beds, lakes, ditches and reservoirs. Once established, it can tolerate a wide variety of conditions and has even moved into some drier areas such as pastures and cropland. This invasive plant easily colonizes disturbed habitats with exposed soil which provide ideal conditions for seed establishment.
 
Invasion History
Originally introduced to North America along the eastern seaboard in the 1800's, purple loosestrife was imported from Europe as an ornamental (decorative) plant. By 1880 this invasive plant had spread across the northeastern United States and was also a common plant in Louisbourg, Cape Breton, Nova Scotia. Purple loosestrife now ranges across Canada, from Newfoundland to British Columbia, and is located in much of the United States. 

Purple loosestrife has also been intentionally introduced for medicinal purposes, including treatment for diarrhea and dysentery. Dried purple loosestrife leaves have also been used to treat ulcers, sores and even heal wounds. 

Another method this alien species has been spread to new areas is by the action of beekeepers. This plant is sometimes used for its quick establishment and nectar yields.

Accidental introductions have also occurred due to ballast water transport.

  
Regional Sightings
Purple loosestrife is currently located thoughout various parts of Nova Scotia and Cape Breton Island. Interestingly, present populations in Nova Scotia are a result of reinvasion of this plant from western populations rather than from the original 1800's population at Louisbourg, which presently has no populations beyond planted gardens (D. McCorquodale, personal communication). 
 
This invasive plant is of particular concern in the Cape Breton Highlands National Park where, like many other invasive species, it threatens the natural biodiversity of the protected lands. 
 
Potential Impacts
Purple loosestrife can be spread very easily from one locale to another. Each plant can produce more than two million seeds annually. The plants are also very aggressive and quickly crowd and out-compete many native species. Purple loosestrife is of special concern in wetlands, where it can extirpate the local vegetation and leave large monoculture stands. These large stands of purple loosestrife may completely alter the physical habitat of the wetlands, and their ability to support a high diversity of insects, birds and other animals.
 
Seeds of this invasive species can remain viable within soil for several years and in water for upwards of twenty months. The size of purple loosestrife seeds also contributes to its success as an invader.  These seeds are very small (about the size of a grain of sand or pepper) and survival rates are also high (60-70%).  Even though this invasive plant species is of concern, it can still be purchased locally as an ornamental plant and if strains of non-sterile plants are available, they can quickly escape from local gardens.
 
Small populations of purple loosestrife can be controlled by physical (cutting and uprooting), and chemical measures (herbicides).  For larger populations it is often necessary to have biological control such as the introduction of predatory insects. 
 
Additional websites related to Purple Loosestrife
 

Literature
  • Stapleton, C.A., McCorquodale, D.B., Sneddon, C., Williams, M., and Bridgland, J.  1998. The Distribution and Potential for Invasiveness of Some Non-Native Vascular Plants in Northern Cape Breton.

 

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