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   Lythrum salicaria (aquatic plant, herb)  français     
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      Flowers of Lythrum salicaria, Yorkshire, UK (Photo: Colin Wilson) - Click for full size   Flowers of Lythrum salicaria in Toronto, Canada (Photo: Colin Wilson) - Click for full size   Lythrum salicaria flowers (Photo: Paul Champion, NIWA) - Click for full size   Lythrum salicaria plants in a ditch in Blenheim, NZ (Photo: Paul Champion, NIWA) - Click for full size   Lythrum salicaria at Lake Horowhenua, NZ (Photo: N. Procter, Horizons Regional Council) - Click for full size
    Taxonomic name: Lythrum salicaria (Linnaeus 1753)
    Synonyms: Lythrum salicaria var. gracilior Turcz., Lythrum salicaria var. tomentosum (P. Mill.) DC., Lythrum salicaria var. vulgare DC.
    Common names: Blutweiderich (German), purple loosestrife (English), rainbow weed (English), salicaire pourpre (French), spiked loosestrife (English)
    Organism type: aquatic plant, herb
    Lythrum salicaria is an erect perennial herb with a woody stem and whirled leaves. It has the ability to reproduce prolifically by both seed dispersal and vegetative propagation. Any sunny or partly shaded wetland is vulnerable to L. salicaria invasion, but disturbed areas with exposed soil accelerate the process by providing ideal conditions for seed germination.
    Lythrum salicaria is an erect, perennial herb with a woody four-sided stem and whorled leaves. Plants are usually covered by a soft down. Leaves are generally opposite, lance-shaped but heart-shaped or rounded at the base. Mature plants can have 30 to 50 stems emerging from a single rootstock and are prolific seed producers. L. salicaria can grow from 1.2 to 3 m high, depending upon conditions. Showy, trimorphic, magenta-coloured flowers, with five to seven petals, are produced throughout most of the summer. Woody stems of plants remain standing during the winter, when the plant is readily identified by its brownish colour and spiral-shaped capsule clusters.
    Similar Species
    Liatris spp., Epilobium angustifolium, Lythrum alatum, Spiraea douglasii, Verbena hastata

    Occurs in:
    riparian zones, ruderal/disturbed, wetlands
    Habitat description
    Lythrum salicaria is capable of invading a variety of wetland habitats, including marshes, river and stream banks, pond edges, lakes, road site ditches, and reservoirs. The plant prefers moist soil with neutral to slightly acidic pH. Once established, however, L. salicaria can exist in a wide range of soil types. Disturbed areas are more prone to invasion because exposed soil is ideal for germination.
    General impacts
    Lythrum salicaria is often reported to outcompete and replace native grasses, sedges, and other flowering plants that provide a higher quality food source and habitat for wildlife. A literature review by Lavoie (2010) of the studies published on purple loosestrife impacts on plants found that 10 out of 11 manipulative studies detected a negative impact on plants. Interestingly all seven observational (field) studies detected no negative impacts. Of the two studies that use both manipulative and observational methods, Yakimowski et al. (2005 in Lavoie, 2010) showed a reduction of the abundance and richness of vascular plant seedlings in purple loosestrife invaded wetlands, while Denoth and Myers (2007 in Lavoie, 2010) concluded that the competitive effect of purple loosestrife on a rare species was not greater than the impact of native plants.

    Lythrum stands can deleteriously impact wildlife habitat used by birds and furbearers. L. salicaria forms dense homogeneous stands that restrict native wetland plant species, including some endangered plants. L. salicaria can overrun wetlands and almost entirely eliminate open water habitat if left untreated. The recreational and aesthetic value of wetlands and waterways is diminished as dense stands of L. salicaria choke waterways and decrease biodiversity. A review of literature by Lavoie (2010) found that out of fourteen animal species or groups studied only six were negatively affected, while others were either not affected or positively affected by purple loosestrife. The strongest negative effects were on tadpoles and the marsh wren (Cistothorus palustris). The American toad (Bufo americanus is also negatively affected by compounds leached from L. salicaria. There have been no studies published on the impacts on fish, mammals or waterfowl (Lavoie, 2010).

    In North American freshwater wetlands, L. salicaria alters decomposition rates and nutrient cycling, water chemistry, leads to reductions in wetland plant diversity, reduces pollination and seed output of the native Lythrum alatum, and reduces habitat suitability for specialized wetland bird species such as black terns, least bitterns, pied-billed grebes, and marsh wrens (Blossey et al., 2001; Fickbohm & Zhu, 2006). L. salicaria effects on wetlands, incurring from lost forage and control costs have been estimated to cost US $28 million per year (Barbier & Knowler, 2006). However, according to Lavoie (2010) “their analysis was apparently based on a previous estimation of the damages calculated by Thompson et al. (1987), damages that were only conjecture.”

    Lythrum salicaria is grown for medicinal uses and planted by beekeepers for its nectar-producing capabilities. It has been used as a herb for diarrhea, dysentery and dried leaves were used to heal wounds, ulcers and sores. L. salicaria is also widely sold as an ornamental in states where regulations do not prohibit its sale and distribution.
    Geographical range
    Native range: Afghanistan, Albania, Algeria, Armenia, Austria, Azerbaijan, Belgium, Bulgaria, China, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, India, Ireland, Israel, Italy, Japan, Jordan, Latvia, Lebanon, Lithuania, Republic of Moldova, Mongolia, Morocco Netherlands, Pakistan, Occupied Palestine Territory, Poland, Portugal, Romania, Russian Federation, Spain, Sweden, Switzerland, Syrian Arabic Republic, Tunisia, Turkey, Ukraine, United Kingdom (UK)
    Known introduced range: Australia, Canada, Ethiopia, New Zealand, South Africa, United States (USA)
    Introduction pathways to new locations
    Floating vegetation/debris:
    Landscape/fauna "improvement":

    Local dispersal methods
    Garden escape/garden waste:
    Water currents:
    Management information
    Preventative measures: The best control measure, however, as with many invasive plants, is to preserve a healthy native ecosystem to prevent or slow invasion.

    Physical: Small infestations (< 100 plants) of L. salicaria can be controlled but cutting and pulling. Cutting should be done just before the plants begin flowering to avoid spreading seed. Pulling should be done by carefully removing all root fragments and disposing of all uprooted plants. Plant materials should be dried and burnt where possible. These fragments and uprooted plants could grow into new plants, possibly making the problem worse. Mowing and burning is ineffective and sometimes makes the problem worse.

    Chemical: Herbicides are most commonly used for quick, effective control of L. salicaria. Spot treating with a glyphosate type herbicide (e.g., Rodeo for wetlands, Roundup for uplands) is effective on older plants. These herbicides may be most effective when applied, as plants are preparing for dormancy, however, mid-summer and late season treatments may be needed to reduce the amount of seed produced. In Canada, only Roundup is registered for the control of Lythrum in terrestrial areas only. Multiple chemical treatments are usually required as new seedlings annually emerge from the seed bank. Chemical treatments may not be desired in sensitive wetland habitats.

    Biological control: Conventional methods such as physical, mechanical or chemical, have continuously failed to curb the spread of Lythrum salicaria or to provide satisfactory control. State and federal agencies as well as private citizens and schools now participate in rearing, release and monitoring of Galerucella beetle species which have been released in 33 states and >1500 wetlands nationwide. Large populations of G. calmariensis have developed in many of the monitored release sites and have caused up to 100% defoliation of L. salicaria. Stem height was reduced 73–85%, percent plant cover was reduced 61–95%, and richness of nontarget plant species increased significantly at four out of five sites. By 2001, L. salicaria stem height and percent cover were reduced 38–81% and 32–74%, respectively, and nontarget plant species richness increased significantly at all five sites. Of the 19 additional sites monitored for 3–5 years post release, 50% (4/8) of the 1997 releases have developed into large G. calmariensis populations and produced severe damage to L. salicari (Blossey et al, 2001; Landis et al, 2003).

    A long-term assessment of biological control impacts after 10 years in central New York State concluded that Galerucella species had significant impacts on plants at the individual level, i.e. shorter plants and reduced flowering rates. However there was no change at the population level: there was no change in overall plant density or in size of stands. Surveys of beetle movement from release site showed only limited spread of beetles to new areas (Grevstad, 2006).

    Integrated management: Results from a study conducted in Manitoba, Canada indicated that an integrated strategy using herbicides (glyphosate and triclopyr amine), combined with biological control G calmariensis outperformed herbicide alone treatments and Galerucella calmariensis alone (Henne et al, 2005).

    Lythrum salicaria reproduces by seed and vegetatively. Flowers require pollination by insects and seeds require open, wet soils and a high temperature to germinate. Flowers are tristylous and pollination restricted to crosses between the style of one length with stamens of the corresponding length. L. salicaria can also spread vegetatively by leftover pieces of trampled, clipped, mowed and pulled plants. A mature plant over 2m tall can have as many as thirty flowering stems and produce large numbers of seeds (up to 3 million seeds per plant has been reported (Thompson et al. 1987)). Seed production is dependent upon age, size and habitat conditions. Seeds are very small and are transported by wind, water, wildlife, vehicles, construction equipment, and humans. Seed survival can be as high as 70%, creating an extensive seed bank. Seedling establishment occurs in late spring and early summer or after soil disturbances including chemical applications. Shoots from vegetative reproduction grow at a rate of approximately 0.3mt per year.
    Lifecycle stages
    Seeds can remain viable in the soil for many years and those submerged in water can remain viable for about 20 months.
    This species has been nominated as among 100 of the "World's Worst" invaders
    Reviewed by: Claude Lavoie, Ecole superieure d'amenagement du territoire et developpement régional (ESAD)
    Compiled by: Profile revision: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Thursday, 15 April 2010

ISSG Landcare Research NBII IUCN University of Auckland