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Datasheet

Lythrum salicaria (purple loosestrife)

Summary

  • Last modified
  • 22 June 2017
  • Datasheet Type(s)
  • Pest
  • Invasive Species
  • Host Plant
  • Preferred Scientific Name
  • Lythrum salicaria
  • Preferred Common Name
  • purple loosestrife
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • L. salicaria, an Old World native, is a highly invasive species of wetlands in North America, beginning to spread rapidly about 140 years after its accidental introduction around 1800. It is a very variable spe...

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Pictures

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PictureTitleCaptionCopyright
Large aggregation of flowering plants, showing the striking purple inflorescences.
TitleInflorescences
CaptionLarge aggregation of flowering plants, showing the striking purple inflorescences.
CopyrightDasa Bastlová
Large aggregation of flowering plants, showing the striking purple inflorescences.
InflorescencesLarge aggregation of flowering plants, showing the striking purple inflorescences.Dasa Bastlová
L. salicaria plants growing in an extremely nutrient-poor habitat of an occasionally flooded sand pit, South Bohemia, Czech Republic.
TitleHabit
CaptionL. salicaria plants growing in an extremely nutrient-poor habitat of an occasionally flooded sand pit, South Bohemia, Czech Republic.
CopyrightDasa Bastlová
L. salicaria plants growing in an extremely nutrient-poor habitat of an occasionally flooded sand pit, South Bohemia, Czech Republic.
HabitL. salicaria plants growing in an extremely nutrient-poor habitat of an occasionally flooded sand pit, South Bohemia, Czech Republic.Dasa Bastlová
L. salicaria seedlings with first pairs of leaves emerging after germination in a litter gap.
TitleSeedlings
CaptionL. salicaria seedlings with first pairs of leaves emerging after germination in a litter gap.
CopyrightDasa Bastlová
L. salicaria seedlings with first pairs of leaves emerging after germination in a litter gap.
SeedlingsL. salicaria seedlings with first pairs of leaves emerging after germination in a litter gap. Dasa Bastlová
New annual shoot emerging from perenial rootstock in spring.
TitleAnnual shoot
CaptionNew annual shoot emerging from perenial rootstock in spring.
CopyrightDasa Bastlová
New annual shoot emerging from perenial rootstock in spring.
Annual shootNew annual shoot emerging from perenial rootstock in spring. Dasa Bastlová
Growth tip of L. salicaria plant 1-2 weeks before inflorescence developed.
TitleGrowth tip
CaptionGrowth tip of L. salicaria plant 1-2 weeks before inflorescence developed.
CopyrightDasa Bastlová
Growth tip of L. salicaria plant 1-2 weeks before inflorescence developed.
Growth tipGrowth tip of L. salicaria plant 1-2 weeks before inflorescence developed. Dasa Bastlová
Roots of L. salicaria.
TitleRoot mass
CaptionRoots of L. salicaria.
CopyrightDasa Bastlová
Roots of L. salicaria.
Root massRoots of L. salicaria. Dasa Bastlová
Galerucella pusilla feeding on L. salicaria plant, with typical holes caused by the herbivore.
TitleNatural enemy
CaptionGalerucella pusilla feeding on L. salicaria plant, with typical holes caused by the herbivore.
CopyrightDasa Bastlová
Galerucella pusilla feeding on L. salicaria plant, with typical holes caused by the herbivore.
Natural enemyGalerucella pusilla feeding on L. salicaria plant, with typical holes caused by the herbivore.Dasa Bastlová
L. salicaria population in eutrophicated fishpond. Plants established on small island with water depth 0-30 cm after water level drawdown, South Bohemia, Czech Republic.
TitleHabit
CaptionL. salicaria population in eutrophicated fishpond. Plants established on small island with water depth 0-30 cm after water level drawdown, South Bohemia, Czech Republic.
CopyrightDasa Bastlová
L. salicaria population in eutrophicated fishpond. Plants established on small island with water depth 0-30 cm after water level drawdown, South Bohemia, Czech Republic.
HabitL. salicaria population in eutrophicated fishpond. Plants established on small island with water depth 0-30 cm after water level drawdown, South Bohemia, Czech Republic.Dasa Bastlová
L. salicaria often grows along road sides in both native and invasive areas.
TitleHabit
CaptionL. salicaria often grows along road sides in both native and invasive areas.
CopyrightDasa Bastlová
L. salicaria often grows along road sides in both native and invasive areas.
HabitL. salicaria often grows along road sides in both native and invasive areas. Dasa Bastlová
L. salicaria is still a very popular ornamental plant in Canada.
TitleOrnamental habit
CaptionL. salicaria is still a very popular ornamental plant in Canada.
CopyrightDasa Bastlová
L. salicaria is still a very popular ornamental plant in Canada.
Ornamental habitL. salicaria is still a very popular ornamental plant in Canada. Dasa Bastlová

Identity

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Preferred Scientific Name

  • Lythrum salicaria L.

Preferred Common Name

  • purple loosestrife

Other Scientific Names

  • Lythrum argyi H.Lév.
  • Lythrum intermedium Ledeb. ex Colla
  • Lythrum salicaria var. gracilior Turcz.
  • Lythrum salicaria var. mairei H.Lév.
  • Lythrum salicaria var. tomentosum (P. Mill) DC.
  • Lythrum salicaria var. vulgare DC.

International Common Names

  • English: purple lythrum; spiked loosestrife
  • Spanish: lysimaquia roja; salicaria
  • French: salicaire commune
  • Portuguese: abre-o-sol; erva-da-vida; quebra-arado; salgueirinha; vassourinha

Local Common Names

  • Canada: purple willowherb; salicaire; swamp loosestrife
  • Germany: Blut- Weiderich; Gemainer Blutweiderich; Gemeiner Blutweiderich
  • Italy: riparella
  • Japan: ezomisohagi
  • Netherlands: Kattestaart
  • Sweden: fackelblomster
  • Turkey: tibbi hevhulma
  • USA: rainbow weed

EPPO code

  • LYTSA (Lythrum salicaria)

Summary of Invasiveness

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L. salicaria, an Old World native, is a highly invasive species of wetlands in North America, beginning to spread rapidly about 140 years after its accidental introduction around 1800. It is a very variable species with an ability to occupy numerous habitats and substrates with the exception of dry places. Its spread and persistence in ecosystems is supported by very high seed production, a vigorous and persistent root system and rapid growth. It is an invasive species and/or noxious weed in almost all states and provinces of Canada and the USA where it is a serious threat to many sensitive wetland ecosystems.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Myrtales
  •                         Family: Lythraceae
  •                             Genus: Lythrum
  •                                 Species: Lythrum salicaria

Notes on Taxonomy and Nomenclature

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L. salicaria is a morphologically variable species, with subspecies sometimes distinguished based mostly on pubescence and origin. With hairy to pubescent leaves, subsp. salicaria is very common in temperate areas and submediterranean and subatlantic Eurasia; the glabrous subsp. intermedium is found from eastern Europe to China and Japan; and the tomentose subsp. tometosum dominates in warmer, Mediterranean regions (Wangerin and Schröter, 1937; Dostál, 1989).

Description

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L. salicaria is a perennial herb 30-200 cm tall with a persistent woody rootstock. In North America and exceptionally in the southern limits of its native range, taller plants (up to 350 cm) can be found. Stems are erect and quadrangular in section with evenly spaced nodes in opposite pairs or in whorls of three. Leaves are 3-10 cm long, sessile, lanceolate to ovate and arising from each node (Thompson et al., 1987; Mal et al., 1992). The stem can be without lateral branches but plants usually form branches in the mid to lower part of the stem (Hegi, 1925). The length and number of lateral branches is variable, depending upon environmental conditions, probably soil nutrient status. Leaves are glabrous to pubescent on the stem and branches, or sub-tomentose on the inflorescence. Inflorescences are purple, in a dense terminal spike up to 1m long. In the first year or under poor nutrient conditions, plants usually have one shoot only, which dies at the end of growing season. In older plants, herbaceous stalks with lateral branches, each with terminal spike of flowers, arise from the rootstock to make a wide-topped crown (Thompson et al., 1987). Fruits are oblong-ovoid capsules (3-4 mm long) with two valves. Seeds are very small (200-400 µm in size, 0.5-0.6 mg in mass), thin-walled with two cotyledons and no endosperm (Thompson et al., 1987). The species is heterostylous with three distinct arrangements of pistils and stamens. The flowers are categorized according to stylar morphs as short-, medium- and long-styled (Mal et al., 1992).

Plant Type

Top of page Broadleaved
Herbaceous
Perennial
Seed propagated
Vegetatively propagated

Distribution

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In its native range, L. salicaria grows in the whole of Europe except high mountainous areas and the most northerly latitudes such as the Faroe Islands, Iceland and northern parts of Scotland, Scandinavia and Russia, with the absolute northern limit being 69°30'N in Norway (Wangerin and Schröter, 1937). The general northern limit is 57°N in the UK, 64°N in Norway, 67°N in Finland, 65°N in European Russia and 61°N in Asian Russia, dropping to 55°N at 97°E and 50°N at Altai, China, near to the Mongolian and Russian borders. The southern limit is 24°N in China and 33°N in Afghanistan and Iran, in dispersed populations. In southern Europe, L. salicaria is common in all countries though is not present in the Balearic Islands and Crete. In Australia, it occurs between 23°S and 42°S and 137°E and 153°E (Wangerin and Schröter, 1937), although distribution data for Australia in USDA-ARS (2007) does not entirely concur with that from Royal Botanic Gardens Sydney (2007). As an exotic species in North America L. salicaria is most common in north-eastern USA and south-eastern Canada (Ontario and Quebec), with a northern limit of 51°N (Mal et al., 1992) and only scattered occurrences up to 56°20'N. In Canada, it is present in all provinces except Yukon and Northwest Territories. In South America, it has only been recorded in Rio Negro, Argentina as an introduced exotic (Wangerin and Schröter, 1937).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

AfghanistanPresentNativeWangerin and Schr÷ter, 1937
ArmeniaPresentNativeUSDA-ARS, 2007
AzerbaijanPresentNativeUSDA-ARS, 2007
China
-AnhuiPresentNativeFlora of China Editorial Committee, 2007
-FujianPresentNativeFlora of China Editorial Committee, 2007
-GansuPresentNativeFlora of China Editorial Committee, 2007
-GuangdongPresentNativeFlora of China Editorial Committee, 2007
-GuangxiPresentNativeFlora of China Editorial Committee, 2007
-GuizhouPresentNativeFlora of China Editorial Committee, 2007
-HainanPresentNativeFlora of China Editorial Committee, 2007
-HebeiPresentNativeFlora of China Editorial Committee, 2007
-HeilongjiangPresentNativeFlora of China Editorial Committee, 2007
-HenanPresentNativeFlora of China Editorial Committee, 2007
-Hong KongPresentNativeFlora of China Editorial Committee, 2007
-HubeiPresentNativeFlora of China Editorial Committee, 2007
-HunanPresentNativeFlora of China Editorial Committee, 2007
-JiangsuPresentNativeFlora of China Editorial Committee, 2007
-JiangxiPresentNativeFlora of China Editorial Committee, 2007
-JilinPresentNativeFlora of China Editorial Committee, 2007
-LiaoningPresentNativeFlora of China Editorial Committee, 2007
-MacauPresentNativeFlora of China Editorial Committee, 2007
-Nei MengguPresentNativeFlora of China Editorial Committee, 2007
-NingxiaPresentNativeFlora of China Editorial Committee, 2007
-QinghaiPresentNativeFlora of China Editorial Committee, 2007
-ShaanxiPresentNativeFlora of China Editorial Committee, 2007
-ShandongPresentNativeFlora of China Editorial Committee, 2007
-ShanxiPresentNativeFlora of China Editorial Committee, 2007
-SichuanPresentNativeFlora of China Editorial Committee, 2007
-TibetPresentNativeFlora of China Editorial Committee, 2007
-XinjiangPresentNativeFlora of China Editorial Committee, 2007
-YunnanPresentNativeFlora of China Editorial Committee, 2007
-ZhejiangPresentNativeFlora of China Editorial Committee, 2007
Georgia (Republic of)PresentNativeUSDA-ARS, 2007
IndiaPresentNativeWangerin and Schr÷ter, 1937
IranPresentNativeMal et al., 1992
IraqPresentNative, ; USDA-ARS, 2007
IsraelPresentNativeUSDA-ARS, 2007
JapanPresentNativeWangerin and Schr÷ter, 1937
-HokkaidoPresentNativeUSDA-ARS, 2007
-HonshuPresentNativeUSDA-ARS, 2007
-KyushuPresentNativeUSDA-ARS, 2007
-ShikokuPresentNativeUSDA-ARS, 2007
LebanonPresentNativeMal et al., 1992
MongoliaPresentNativeWangerin and Schr÷ter, 1937
PakistanPresentNativeMal et al., 1992
SyriaPresentNativeMal et al., 1992
TaiwanPresentNative
TurkeyPresentNativeWangerin and Schr÷ter, 1937

Africa

AlgeriaPresentNativeWangerin and Schr÷ter, 1937; Mal et al., 1992
EthiopiaPresentNativeMal et al., 1992
MoroccoPresentNativeWangerin and Schr÷ter, 1937
TunisiaPresentNativeWangerin and Schr÷ter, 1937

North America

Canada
-AlbertaPresentIntroducedMal et al., 1992
-British ColumbiaPresentIntroducedMal et al., 1992
-ManitobaPresentIntroduced1896Stuckey, 1980; Mal et al., 1992
-New BrunswickPresent, few occurrencesIntroducedMal et al., 1992
-Newfoundland and LabradorPresentIntroducedMal et al., 1992
-Northwest TerritoriesAbsent, intercepted onlyIntroducedMal et al., 1992
-Nova ScotiaPresent, few occurrencesIntroduced1883Stuckey, 1980; Mal et al., 1992
-NunavutPresentIntroducedStuckey, 1980; Mal et al., 1992
-OntarioWidespreadIntroduced1884 Invasive Stuckey, 1980; Mal et al., 1992; Treberg and Husband, 1999
-Prince Edward IslandPresentIntroducedMal et al., 1992
-QuebecWidespreadIntroduced1884 Invasive Stuckey, 1980; Mal et al., 1992
-SaskatchewanPresentIntroducedMal et al., 1992
-Yukon TerritoryAbsent, intercepted onlyIntroducedMal et al., 1992
USA
-AlabamaPresentIntroduced Invasive USDA-NRCS, 2007
-ArkansasPresentIntroduced Invasive USDA-NRCS, 2007
-CaliforniaPresentIntroduced1948 Invasive Stuckey, 1980; USDA-NRCS, 2007
-ColoradoPresentIntroduced1978Stuckey, 1980; USDA-NRCS, 2002
-ConnecticutPresentIntroduced1895 Invasive Stuckey, 1980; USDA-NRCS, 2002
-DelawarePresentIntroducedUSDA-NRCS, 2002
-FloridaPresentIntroduced Invasive ,
-IdahoPresentIntroduced1972Stuckey, 1980; USDA-NRCS, 2002
-IllinoisPresentIntroduced1903 Invasive Stuckey, 1980; USDA-NRCS, 2002
-IndianaPresentIntroduced1914 Invasive Stuckey, 1980; USDA-NRCS, 2002
-IowaPresentIntroduced Invasive USDA-NRCS, 2002
-KansasPresentIntroduced1968Stuckey, 1980; USDA-NRCS, 2002
-KentuckyPresentIntroduced1896Stuckey, 1980; USDA-NRCS, 2002
-MainePresentIntroducedUSDA-NRCS, 2002
-MarylandPresentIntroduced1910Stuckey, 1980; USDA-NRCS, 2002
-MassachusettsPresentIntroduced1831 Invasive Stuckey, 1980; USDA-NRCS, 2002
-MichiganPresentIntroduced1839 Invasive Stuckey, 1980; USDA-NRCS, 2002
-MinnesotaPresentIntroduced1920-1939 Invasive Stuckey, 1980; USDA-NRCS, 2002
-MississippiPresentIntroduced Invasive USDA-NRCS, 2002
-MissouriPresentIntroducedbefore 1936 Invasive Stuckey, 1980; USDA-NRCS, 2002
-MontanaPresentIntroducedUSDA-NRCS, 2002
-NebraskaPresentIntroduced1973Stuckey, 1980; USDA-NRCS, 2002
-NevadaPresentIntroduced Invasive USDA-NRCS, 2002
-New HampshirePresentIntroduced1875 Invasive Stuckey, 1980; USDA-NRCS, 2002
-New JerseyPresentIntroduced1840-1859Stuckey, 1980; USDA-NRCS, 2002
-New MexicoPresentIntroduced Invasive ,
-New YorkPresentIntroduced1920-1939 Invasive Stuckey, 1980; USDA-NRCS, 2002
-North CarolinaPresentIntroduced1885 Invasive Stuckey, 1980; USDA-NRCS, 2002
-North DakotaPresentIntroduced Invasive USDA-NRCS, 2002
-OhioPresentIntroduced1902 Invasive Stuckey, 1980; USDA-NRCS, 2002
-OklahomaPresentIntroduced Invasive USDA-NRCS, 2002
-OregonPresentIntroduced Invasive USDA-NRCS, 2002
-PennsylvaniaPresentIntroduced1901 Invasive Stuckey, 1980; USDA-NRCS, 2002
-Rhode IslandPresentIntroduced1905Stuckey, 1980; USDA-NRCS, 2002
-South CarolinaPresentIntroduced Invasive ,
-South DakotaPresentIntroduced Invasive USDA-NRCS, 2002
-TennesseePresentIntroduced Invasive USDA-NRCS, 2002
-TexasPresentIntroducedUSDA-NRCS, 2002
-UtahPresentIntroduced1943Stuckey, 1980; USDA-NRCS, 2002
-VermontPresentIntroduced1898 Invasive Stuckey, 1980; USDA-NRCS, 2002
-VirginiaPresentIntroducedUSDA-NRCS, 2002
-WashingtonPresentIntroduced Invasive USDA-NRCS, 2002
-West VirginiaPresentIntroduced1858Stuckey, 1980; USDA-NRCS, 2002
-WisconsinPresentIntroduced1928 Invasive USDA-NRCS, 2002
-WyomingPresentIntroducedUSDA-NRCS, 2002

South America

ArgentinaPresentWangerin and Schr÷ter, 1937; Torres and Puntieri, 2015

Europe

AlbaniaPresentNativeRoyal Botanic Garden Edinburgh, 2007
AustriaPresentNativeRoyal Botanic Garden Edinburgh, 2007
BelarusPresentNativeUSDA-ARS, 2007
BulgariaPresentNativeRoyal Botanic Garden Edinburgh, 2007
CroatiaPresentNativeWangerin and Schr÷ter, 1937
Czech RepublicPresentNativeRoyal Botanic Garden Edinburgh, 2007
DenmarkPresentNativeRoyal Botanic Garden Edinburgh, 2007
EstoniaPresentNativeUSDA-ARS, 2007
Faroe IslandsAbsent, formerly presentWangerin and Schr÷ter, 1937
FinlandPresentNative Not invasive Wangerin and Schr÷ter, 1937
FrancePresentNativeRoyal Botanic Garden Edinburgh, 2007
GermanyPresentNative, ; Royal Botanic Garden Edinburgh, 2007; USDA-ARS, 2007
GreecePresentNativeRoyal Botanic Garden Edinburgh, 2007
HungaryPresentNativeRoyal Botanic Garden Edinburgh, 2007
IcelandAbsent, intercepted onlyNativeWangerin and Schr÷ter, 1937
IrelandPresentNativeWangerin and Schr÷ter, 1937
ItalyPresentNativeThompson et al., 1987
LatviaPresentNativeUSDA-ARS, 2007
LithuaniaPresentNativeUSDA-ARS, 2007
MoldovaPresentNativeUSDA-ARS, 2007
NetherlandsPresentNativeRoyal Botanic Garden Edinburgh, 2007
NorwayPresentNativeRoyal Botanic Garden Edinburgh, 2007
PolandPresentNativeRoyal Botanic Garden Edinburgh, 2007
PortugalPresentNativeRoyal Botanic Garden Edinburgh, 2007
RomaniaPresentNativeRoyal Botanic Garden Edinburgh, 2007
Russian FederationPresentNativeWangerin and Schr÷ter, 1937
-Central RussiaPresentNativeRoyal Botanic Garden Edinburgh, 2007
-Eastern SiberiaPresentNativeUSDA-ARS, 2007
-Northern RussiaPresentNativeRoyal Botanic Garden Edinburgh, 2007
-Russian Far EastPresentNativeUSDA-ARS, 2007
-Southern RussiaPresentNativeUSDA-ARS, 2007
SerbiaPresentNativeUSDA-ARS, 2007
SlovakiaPresentNativeRoyal Botanic Garden Edinburgh, 2007
SpainPresentNativeRoyal Botanic Garden Edinburgh, 2007
-Balearic IslandsAbsent, intercepted onlyWangerin and Schr÷ter, 1937
SwedenPresentNativeRoyal Botanic Garden Edinburgh, 2007
SwitzerlandPresentNativeStuckey, 1980; Mal et al., 1992
UKPresentNativeRoyal Botanic Garden Edinburgh, 2007
UkrainePresentNativeUSDA-ARS, 2007

Oceania

Australia
-New South WalesPresentNativeWangerin and Schr÷ter, 1937; Royal Botanic Garden Sydney, 2007
-QueenslandPresentNativeWangerin and Schr÷ter, 1937; Royal Botanic Garden Sydney, 2007
-South AustraliaPresentNative Invasive Royal Botanic Garden Sydney, 2007
-TasmaniaPresentNativeWangerin and Schr÷ter, 1937; Mal et al., 1992; Royal Botanic Garden Sydney, 2007
-VictoriaPresentNativeWangerin and Schr÷ter, 1937; Royal Botanic Garden Sydney, 2007
New ZealandPresentIntroducedMal et al., 1992

History of Introduction and Spread

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The first mention of L. salicaria in North America was in 1814 (Stuckey, 1980) and it was thought to have been introduced either in ship ballast or with sheep wool to the eastern coast around 1800 (Stuckey, 1980; Thompson et al., 1987). L. salicaria spread slowly along rivers, canals and ditches and moved westwards along the newly constructed Erie Canal (Thompson et al., 1987), and the history of further spread and distribution in North America is well documented (e.g. Stuckey, 1980). From 1850 to 1900, L. salicaria was probably re-introduced with successive waves of European immigrants as a medicinal herb (Thompson et al., 1987) but it was not until the 1930s that the first monocultural populations and rapid expansion of this species westward were observed (Stuckey, 1980), some 140 years after first being introduced. In the 1940s, beekeepers and honey producers began to realize the potential of using this species as a bee forage (Pellett, 1977; Hayes, 1979) and there are reports of beekeepers deliberately spreading L. salicaria seeds along streams and rivers in order to increase the density and number of flowering populations (Thompson et al., 1987). By 1985, L. salicaria was recorded in all states of the USA and southern provinces of Canada between 37°N and 50°N (Edwards et al., 1995), with the highest frequency along the St Lawrence River.

Risk of Introduction

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Original introductions were accidental, with seed as a contaminant of ballast water, wool and/or live sheep, and these could still be pathways for introduction of this invasive plant elsewhere. Also, commercial nurseries sell cultivars of L. salicaria advertized as being sterile, although research has shown that these cultivars are fertile both when crossed with themselves and with wild L. salicaria populations (USDA-NRCS, 2007). L. salicaria can still be bought from numerous suppliers of ornamental plant seed even though it is a noxious weed in many states of North America. At particular risk may be wetlands of temperate areas of South America where it is not yet present, and also in South Africa (Mgidi et al., 2007).

Habitat

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Where native in Europe, L. salicaria has a wide ecological range, but is generally a species of wet sites. It persists in littoral vegetation, fishponds or streams (Hejný, 1960), rock pools (Hæggström and Skytén, 1987), mudflats (Toivonen and Bäck, 1989), fen meadows, swamp basins, woodlands or open woody margins (Wheeler, 1980a). In England, L. salicaria is a frequent species in open carrs (wet shrub communities) with very rich vegetation and fluctuating water levels, moist woody water margins, beneath woods, and gravel with permanent water 10-15 cm below the surface during the summer (Pearsall, 1918). Usually it is described as a component of early successional vegetation on slightly disturbed or open sites with periodical fluctuations in the water level (Hejný, 1960).

As an exotic species in North America L. salicaria occurs in similar habitats, including littoral vegetation of freshwater marshes and stream margins (Thompson et al., 1987), sedge meadows (Larson, 1989) and road sides (Isabelle et al., 1987). However, in contrast to European native habitats, it is also found in wetlands with high water levels (40 cm or more) in North America (Rawinski and Malecki, 1984; Bastlová-Hanzélyová, 2001). In north-eastern and north-central USA and adjacent provinces of Canada, alluvial floodplains are described as the optimal habitat (Thompson et al., 1987).

Habitat List

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CategoryHabitatPresenceStatus
Freshwater
Freshwater Present, no further details Harmful (pest or invasive)
Irrigation channels Secondary/tolerated habitat Harmful (pest or invasive)
Ponds Secondary/tolerated habitat Harmful (pest or invasive)
Littoral
Coastal areas Secondary/tolerated habitat Harmful (pest or invasive)
Coastal areas Secondary/tolerated habitat Natural
Terrestrial-managed
Cultivated / agricultural land Secondary/tolerated habitat Harmful (pest or invasive)
Managed forests, plantations and orchards Secondary/tolerated habitat Harmful (pest or invasive)
Managed grasslands (grazing systems) Present, no further details Harmful (pest or invasive)
Rail / roadsides Secondary/tolerated habitat Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Natural forests Secondary/tolerated habitat Harmful (pest or invasive)
Natural grasslands Secondary/tolerated habitat Harmful (pest or invasive)
Natural grasslands Secondary/tolerated habitat Natural
Riverbanks Principal habitat Harmful (pest or invasive)
Riverbanks Principal habitat Natural
Wetlands Principal habitat Harmful (pest or invasive)
Wetlands Principal habitat Natural

Hosts/Species Affected

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As an exotic invasive species, L. salicaria is not generally a weed of agricultural land as it prefers moist to wet habitats, but it may occur at disturbed edges of crop fields in the vicinity of wetlands. The establishment of L. salicaria adjacent to stands of wild rice (Zizania aquatica) in northern California and Wisconsin, USA, means that it may be or become a pest of this crop (Thompson et al., 1987).

Biology and Ecology

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Genetics

Base chromosome number for L. salicaria has been recorded as n=15 (2n=30), n=25 (2n=50) and n=30 (2n=60), with n=29 (2n=58) rarely observed (Graham and Cavalcanti, 2001). The lowest chromosome counts of 2n=30 were found in Asia, Israel (Dulberger, 1968) and Japan. Intermediate ploidy levels (2n=50) were observed in populations found in northern Germany, north-east Poland and Scandinavia (Mal et al., 1992), while the highest counts of 2n=60 were found throughout Europe; the Czech Republic, Denmark, France, The Netherlands, Norway, Poland, Slovakia and Sweden (Mal et al., 1992). Aneuploids have also been recorded as 2n=45 and 2n=59 (Mal et al., 1992). Chromosome counts reported from North America are 2n=50 and 2n=60 in Ontario, and 2n=60 in Quebec (Mal et al., 1992), indicated Europe rather than Asia as the source of North American germplasm.

Physiology and Phenology

Comprehensive research has been undertaken on the ecophysiology of L. salicaria (Shamsi and Whitehead, 1974a, b; Shamsi, 1974; Shamsi, 1976; Shamsi and Whitehead, 1977a, b), involving basic life requirements and the influence of environmental conditions. L. salicaria is very responsive to differences in nutrient supply, by increasing the root:shoot ratio as nutrient supply decreases, at the expense of dry weight of the stem rather than leaves (Shamsi and Whitehead, 1977a). The proportion of leaves remained similar at all nutrient concentrations tested, although with decreasing nutrient concentration the plant dry weight and number of lateral branches decreased progressively together with a reduction of flowering and fruiting (Shamsi and Whitehead, 1977a).

L. salicaria plants grown at 70% full light exhibit increased leaf area but produced less dry mass and fewer lateral branches as compared to plants grown under full light, and flower later and have smaller fruits with fewer seeds though seed weight was constant (Shamsi and Whitehead, 1974b). Distribution of dry weight between roots, stem and leaves was only moderately influenced by light intensity, with roots forming a high proportion relative to stems and their proportion remained the same, whereas the proportion of leaves increased slightly during ontogeny. Variation in day length had a dramatic effect on growth of L. salicaria plants with 13 h day length appearing to be optimal for the elongation of the main stem, lateral branches and overall growth.

No significant effect of water level on growth and biomass production of L. salicaria was reported from either field (Edwards et al., 1995; Edwards, 1996) or greenhouse experiments (Stevens et al., 1997), although decreasing water availability reduced plant height (Edwards et al., 1995; Stevens and Peterson, 1996). Total biomass content is significantly lower in relatively dry treatments and total stem diameter and porosity and root water content were higher in submersed portions of flooded stems, in both the flooded and the intermediate treatments. Increase in stem porosity and diameter was caused by the presence of aerenchyma in flooded plant parts.

Seed germination occurs in late spring and early summer, beginning generally in late June to early July and continues until end of August or beginning of September. Under experimental conditions the plant usually takes about 10 weeks to flower but under natural field conditions flowering may take up to 12 months. Maturation of the main inflorescence axis follows an acropetal sequence, i.e. basal capsules mature first while the distal part of the inflorescence is still flowering and the plant is green and leafy. The maturation of the axillary lateral inflorescences (on the lateral branches) follows a basipetalous (centrifugal) sequence. Aboveground parts of the plant die back in late autumn and new shoots emerge from the overwintering buds at the top of the rootstock. However, there is also evidence that a minority of established plants in North America can remain dormant above ground for a year and then resume growth in the next growing season (Thompson et al., 1987).

Reproductive Biology

L. salicaria reproduces mostly by seed, although vegetative propagation from rooting nodes has also been observed (Thompson et al., 1987). It is a self-incompatible species. Seed production is dependent on the age, size and vigour of the plant and a single stem can generally produce 900-1000 capsules (Shamsi and Whitehead, 1974a; Thompson et al., 1987), with 83-130 seeds per capsule (Mal et al., 1992). Taking into account the number of stems arising from root, Thompson at al. (1987) estimated the average seed production per plant to be in the order of 2,700,000. Seed viability is very high under laboratory conditions, and seed will even germinate after storage for several years (Wangerin and Schröter, 1937). Although there is no information on the longevity and viability of seeds under field conditions, there can be very large numbers in the seed bank. Welling and Becker (1990) studied seed bank dynamics in North American wetlands and found the mean density of seeds to be 410,000 per m² in the top 5 cm of wetland soil with 37% of these found below a depth of 2 cm.

Optimum temperature for germination is 15-20°C with no germination occurring below 14°C (Shamsi and Whitehead, 1974a). In darkness, germination starts at 20°C and increases rapidly to a maximum at 30°C. Due to these relatively high temperature requirements, L. salicaria seeds can only germinate in late spring or summer in temperate regions. Sand and clay media reduced and delayed germination by 5 and 10 days, respectively, compared to germination on filter paper. L. salicaria can germinate successfully from pH 4 (Shamsi and Whitehead, 1974a) to pH 9.1 (Thompson et al., 1987). Day length (9-16 h light) and different levels of nutrition have no significant effect on the rate or final germination.

Environmental Requirements

L. salicaria is a typical helophyte usually occurring in wet, marshy places, stream banks and ditches at altitudes below 600 m and in low-lying coastal areas (Mal et al., 1992). Temperature is probably the limiting factor to growth and distribution in northern parts of North America (Shamsi, 1974; Thompson et al., 1987). For germination, disturbed sites or open, moist substrates such as water or water edges are necessary and once established, populations may persist for long periods under different conditions at a particular site. It grows better in habitats covered by water temporarily in the spring and which are moist but not covered by water during its active growing period. Optimum substrates for the growth of L. salicaria are moist soils of neutral to slightly acid pH (Shamsi and Whitehead, 1977b). Thompson et al. (1987) found plants growing in a wide range of soil textures and types in North America, from rock crevasses to gravel, sand, clay, organic soils and even crushed-rock ballast on a railroad bridge, suggesting that moisture is the most important factor for growth and reproduction. In the field, L. salicaria can survive in 50% of full sun, but declines in vigour and fails to reproduce at lower light levels (Thompson et al., 1987).

Associations

Wheeler (1980a) listed many species in rich-fen vegetation, usually sedge and fen meadow plant communities, where L. salicaria occurs, in association with Caricion davallianae, Junco-Molinion spp., Magnocaricion spp., Phragmition communis and Phragmition spp. In carrs (wet shrub communities), it is found with Alnion glutinosae and Salicion cinereae (mire forests) on nutrient-rich substrates in England and Wales. In the Czech Republic, L. salicaria is a principal species of the Magnocaricion alliance, in association with Caricetum ripario-acutiformis (Hejný, 1960; Dubyna et al., 1993) and other plant species such as Glyceria fluitans, Lysimachia vulgaris, Oenanthe aquatica or Sium latifolium. L. salicaria is facultatively mycorrhizal (Stevens and Peterson, 1996). Although the young foliage of L. salicaria is palatable to grazing animals, both wild and domesticated, the mature plant is much less frequently browsed. Browsing by wildlife may result in a reduction of growth and biomass of L. salicaria (Anderson, 1995), although lower palatability gives it a comparative advantage over more palatable native grasses and sedges in North America and this is thought to be one of the keys reasons for its success as an invasive species of pastures (Thompson et al., 1987).

Climate

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ClimateStatusDescriptionRemark
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
D - Continental/Microthermal climate Tolerated Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)
Df - Continental climate, wet all year Tolerated Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Air Temperature

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Parameter Lower limit Upper limit
Mean annual temperature (ºC) 5 18
Mean maximum temperature of hottest month (ºC) 13 36
Mean minimum temperature of coldest month (ºC) -4 6

Rainfall

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ParameterLower limitUpper limitDescription
Mean annual rainfall5001700mm; lower/upper limits

Soil Tolerances

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Soil drainage

  • impeded
  • seasonally waterlogged

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Bayeriola salicariae Herbivore Stems
Galerucella calmariensis Herbivore Inflorescence/Leaves
Galerucella pusilla Herbivore Inflorescence/Leaves
Hylobius transversovittatus Herbivore Roots
Nanophyes brevis Herbivore Inflorescence/Seeds
Nanophyes marmoratus Herbivore Inflorescence/Leaves/Seeds

Notes on Natural Enemies

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Batra et al. (1986) identified 120 species of phytophagous insects associated with L. salicaria from surveys in Europe (Italy, Austria, Norway, Sweden and Croatia). This list includes 14 species probably restricted to Lythrum spp. and 64 species of floral visitors associated with L. salicaria. One of the most common of all phytophages was the univoltine weevil Nanophyes marmoratus (Coleoptera: Curculionidae) attacking fruits and destroying up to 69% of the ovules of some plants (Batra et al., 1986). The multivoltine chrysomelids, Pyrrhalta calmariensis [Galerucella calmariensis] and Pyrrhalta pusilla [Galerucella pusilla] (Coleoptera: Chrysomelidae) were patchily abundant in Italy, Austria and Croatia, where dense populations on some plants cause significant (ca. 50%) defoliation. Dasineura salicariae (Diptera: Cecidomyiidae), specific to L. salicaria, is widespread in the cool climates of northern and central Europe, forming galls in apical and axillary meristems which effectively prevent flowering and branching. These galls can reduce foliage production by 75% and reduce the growth of inflorescences and seed production by 80% (Batra et al., 1986). In both Europe and North America the open flowers of L. salicaria are a rich nectar and pollen resource for a wide variety of beneficial insects including pollinating bees, adult parasitic wasps and syrphid flies, as well as for the adults of many phytophagous and saprophagous insects.

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)

Long distance dispersal is largely by means of floating seeds (Thompson et al., 1987). Seeds are also light enough to be dispersed by strong wind, but the role of this kind of dispersal seems to be limited and restricted to short distances only, up to 10 m from the parent plant (Thompson et al., 1987).

Vector Transmission (Biotic)

The seeds are likely to be dispersed in mud adhering to aquatic wildlife or via consumption by waterfowl, or attached to livestock, all-terrain vehicle tyres and human footwear, although there is no direct evidence to support any of these potential pathways (Thompson et al., 1987).

Accidental Introduction

In the early 1800s, L. salicaria was probably repeatedly introduced into North America across the Altlantic with ship ballast and imported raw wool or on live sheep (Stuckey, 1980; Thompson et al., 1987).

Intentional Introduction

Purposeful introduction could have occurred at a very early time and has become an increasing problem in the recent history of spread. L. salicaria was valued as a medicinal herb in northern Europe and seeds were probably brought in by immigrants in the 1800s. L. salicaria seeds or rootstalks may also been brought to North America by horticulturists as an ornamental plant for gardens and cultivated sites (Thompson et al., 1987) and are still widely available today. In both North America and Europe, apiculture journals and suppliers have offered seed for sale and provided advice for the growing of L. salicaria and probably distributed plants in some regions.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Botanical gardens and zoos Yes USDA-NRCS, 2007
Flooding and other natural disasters Yes Yes Thompson et al., 1987
ForageIn hay as feed Yes Thompson et al., 1987
Harvesting fur, wool or hairOn imported wall Yes Thompson et al., 1987
Internet sales Yes USDA-NRCS, 2007
Live food or feed tradeOn live sheep Yes Thompson et al., 1987
Medicinal useImmigrants bringing it as a medicinal plant Yes
Nursery trade Yes USDA-NRCS, 2007
Ornamental purposes Yes USDA-NRCS, 2007

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsBoots Yes Thompson et al., 1987
Land vehiclesAll kinds of treads Yes Thompson et al., 1987
LivestockStuck on mud to, also, more importantly on wild animals Yes Thompson et al., 1987
Machinery and equipment Yes Thompson et al., 1987
MailCommercial nurseries, botanical gardens Yes Thompson et al., 1987
Plants or parts of plants Yes Thompson et al., 1987
Ship ballast water and sediment Yes Thompson et al., 1987
Soil, sand and gravelShip ballast; ship transport Yes Yes Thompson et al., 1987
Water Yes Yes Thompson et al., 1987

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Flowers/Inflorescences/Cones/Calyx seeds No No
Growing medium accompanying plants roots; seeds No No
Roots roots; seeds No No
Stems (above ground)/Shoots/Trunks/Branches seeds No No
True seeds (inc. grain) seeds No No
Plant parts not known to carry the pest in trade/transport
Bark
Bulbs/Tubers/Corms/Rhizomes
Fruits (inc. pods)
Leaves
Seedlings/Micropropagated plants
Wood

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Negative
Crop production None
Cultural/amenity Negative
Economic/livelihood Negative
Environment (generally) Negative
Fisheries / aquaculture Negative
Forestry production None
Human health None
Livestock production Negative
Native flora Negative
Rare/protected species Negative
Tourism Positive
Trade/international relations Negative
Transport/travel None

Impact

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Where L. salicaria is common, direct economic losses are caused by reduced livestock stocking rates and reduction of water flow in irrigation systems. Livestock forage value was reduced in meadows where L. salicaria had established monospecific stands and the palatability of cut hay containing L. salicaria is reduced. L. salicaria is a threat to wetland pastures that typically occur along floodplains and on the peripheries of glacial marshes in central USA and is threatening the production of wild rice (Zizania aquatica) in such areas (Thompson et al., 1987).

Economic Impact

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Where L. salicaria is common, direct economic losses are caused by reduced livestock stocking rates and reduction of water flow in irrigation systems. Livestock forage value was reduced in meadows where L. salicaria had established monospecific stands and the palatability of cut hay containing L. salicaria is reduced. L. salicaria is a threat to wetland pastures that typically occur along floodplains and on the peripheries of glacial marshes in central USA and is threatening the production of wild rice (Zizania aquatica) in such areas (Thompson et al., 1987). Also, of course, there are significant negative impacts from control efforts, and positive impacts from trading in L. salicaria as an ornamental. Barbier and Knowler (2006) used a model to compare these opposing values using L. salicaria as an example, and concluded that there was a need for an “introducers’ pay” tax to put limits on the uncontrolled spread of trade in invasive species, and spread of the species themselves.

Environmental Impact

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Impact on Habitat

The dominance of L. salicaria in wetland vegetation causes significant changes in wetland function by altering the timing of litter input and downstream phosphorus load, resulting in accelerated eutrophication of water bodies (Emery and Perry, 1996), with effects on organic matter distribution and soil nitrogen cycling (Fickbohm and Zhu, 2006).

Impact on Biodiversity

Negative impact of L. salicaria on diversity of plant communities has not been clearly demonstrated and results of various evaluations depend upon the ecological criteria that are used, and some studies even indicate a positive effect of L. salicaria invasion on plant diversity (e.g. Hagar and Vinebrooke, 2004). L. salicaria may suppress the biomass of many wetland plants when germinated and grown simultaneously under laboratory conditions, but it appears to be negatively affected by competition in the field (Shamsi and Whitehead, 1974a, b 1977; Rawinski and Malecki, 1984; Anderson, 1995). Farnsworth and Ellis (2001) quantified multiple stand characteristics of L. salicaria and associated vegetation and found that species richness and stem density of other species were not significantly correlated with the density or percentage cover of L. salicaria stems. With increasing density and total biomass of L. salicaria, the biomass of other species remained constant, or increased at a slower rate and thus appeared to decrease relative to L. salicaria. Anderson (1995) and Treberg and Husband (1999) found no significant relationships between species richness and percentage cover of L. salicaria although the total biomass of all species was significantly, negatively correlated with total biomass of L. salicaria. Once established, individual L. salicaria plants can live for over 20 years (Thompson et al., 1987; Anderson, 1995) and often produce an increasing number of stems each year which may eventually negatively affect community composition and stability.

L. salicaria is an important species for wildlife, with white-tailed deer, muskats, rabbits and several birds including red-winged blackbirds (Agelaius phoeniceus) all observed feeding on L. salicaria (Rawinski and Malecki, 1984; Anderson, 1995). L. silicaria-dominated wetlands were also found to be inadequate breeding habitats for some species of native birds in North America (Maddox and Wiedenmann, 2006). Also, a recent study attempted to assess the effects of invasion on amphibian populations and although results were not significant, Brown et al. (2006) concluded that threats on amphibian populations and food webs may be underestimated, and warrant further investigation.

Social Impact

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Wetlands with tall, dense stands dominated by invading L. salicaria can be impenetrable to boats (Thompson et al., 1987) and would reduce hunting opportunities (Blossey et al., 2002).

Risk and Impact Factors

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Impact mechanisms

  • Competition - monopolizing resources
  • Rapid growth

Impact outcomes

  • Altered trophic level
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Modification of hydrology
  • Modification of nutrient regime
  • Modification of successional patterns
  • Monoculture formation
  • Negatively impacts agriculture
  • Negatively impacts aquaculture/fisheries
  • Negatively impacts livelihoods
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
  • Transportation disruption

Invasiveness

  • Abundant in its native range
  • Fast growing
  • Has a broad native range
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Highly adaptable to different environments
  • Highly mobile locally
  • Long lived
  • Proved invasive outside its native range

Likelihood of entry/control

  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally deliberately

Uses

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The profuse and attractive floral displays of L. salicaria make the plant well known to gardeners. Its presence is reported in early American gardens (Thompson et al., 1987) and its inclusion in garden and border planting continues throughout Canada and the USA even today, with various cultivars sold in nurseries as potted plants. In areas where it is widespread, L. salicaria is an important source of bee forage, being very attractive to honey bees, although the exact economic benefits of flower production are not known. L. salicaria is now seldom used as a medicinal plant in Europe, but it was highly recommended in early medicine as an astringent, tonic and a blood clotting agent (Thompson et al., 1987), and still has numerous uses today in many parts of Asia, such as a treatment against diarrhoea, chronic intestinal catarrh, haemorrhoids, eczema, varicose veins and bleeding of the gum sin Turkey (Tunalier et al., 2007).

Uses List

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Animal feed, fodder, forage

  • Invertebrate food

Environmental

  • Landscape improvement

Fuels

  • Fuelwood

General

  • Botanical garden/zoo
  • Ornamental

Human food and beverage

  • Honey/honey flora

Medicinal, pharmaceutical

  • Source of medicine/pharmaceutical
  • Traditional/folklore

Similarities to Other Species/Conditions

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In North America, L. salicaria may sometimes be confused with Desmodium canadense, Epilobium angustifolium, Epilobium ciliatum, Liatris spicata and Verbena hastata. In Europe it may be confused with Epilobium angustifolium, Epilobium ciliatum or Lythrum alatum. However, the combination of habitat, square stem and opposite leaves should distinguish L. salicaria from other species.

Prevention and Control

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Control

Cultural control

Use of flooding and competition from other plant species has been attempted with very limited success. However, flooding to a depth of up to 50 cm for two years had little effect on the stature and reproductive characteristics of L. salicaria and appeared not be a successful method of control (Malecki and Rawinski, 1985). High water level may additionally present stresses for native plant communities. Also, plant competition was only partly successful and results differed greatly depending on the plant species used. Echinochloa frumentacea (Japanese millet) and Polygonum lapathifolium (nodding smartweed) grew well and out-competed L. salicaria (Rawinski, 1982) although Echinochloa walteri (Walter's millet) and Phalaris arundinacea (reed canarygrass) were unsuccessful (Malecki and Rawinski, 1985; Balogh, 1993). Typha x glauca is another potential species on permanently flooded sites (water level always greater than 40 cm) possibly combined with damage by carp (Rawinski and Malecki, 1984). Growth form, habitat type and phenology of L. salicaria indicate that it will not be susceptible to control with fire (Thompson et al., 1987).

Mechanical control

Mechanical control, such as mowing, ploughing or hand-pulling give only limited success (Malecki and Rawinski, 1985). Small populations may be successfully controlled by hand pulling, but this method should be avoided after flowering so as not to scatter seeds and plants should be bagged at the site to avoid fragments being dropped along the exit route. Burning is the preferred method for disposal of cut or pulled plants. The date of cutting has an important role in reducing the number of shoots but does not result in permanent control.

Chemical control

Use of herbicides, mostly spot applications of glyphosate, appears to be the most efficient means of control of L. salicaria (Malecki and Rawinski, 1985; Balogh, 1993; Welling and Becker, 1993), although glyphosate and triclopyr amine were both used in Manitoba with success (Henne et al., 2005), and these and several other chemicals were tested alone and in mixtures with success, including triclopyr, 2,4-D dimethylamine and imazapyr (Knezevic et al., 2004). Using glyphosate alone, the timing of applications is important, with late flowering application (13 July) being the most effective with nearly 100% of shoot reduction, as compared to application during the vegetative or early flowering (13 June) stage (Malecki and Rawinski, 1985). Studies on the seed bank dynamics of L. salicaria have shown that for its effective control, a control programme has to operate for a number of years. Single treatments had only a temporary effect due to resprouting from the roots and new plants becoming recruited from the seed bank (Welling and Becker, 1990). The need for repeated chemical treatments over several years can lead to environmental chemical contamination and this type of control has risks associated with negative impacts on native and often threatened flora.

Biological control

Since the 1990s, great attention has been paid to the biological control of L. salicaria in Canada and the USA. In 1992/3, three insects were approved for release as L. salicaria control agents after laboratory tests in Europe and North America (Hight et al., 1995), although as many as 59 species of phytophagous insects were collected on L. salicaria plants in the north-eastern USA (Hight, 1990). The released agents were two herbivorous insects, Galerucella calmariensis and Galerucella pusilla (Coleoptera: Chrysomelidae) and a root weevil Hylobius transversovittatus (Coleoptera: Curculionidae) and all three established successfully (Hight et al., 1995; Blossey et al., 2002). Malecki et al. (1993) predicted reduction of L. salicaria abundance to approximately 10% of original levels, however, it is expected that plant refugia will remain at sites with high water levels which prevent the development of the root-mining weevil and limit recruitment of the Galerucella spp, and also that plants growing in the shade will also be less likely to be attacked by these biological control agents. They were released in 1684 different wetlands in the USA invaded by L. salicaria (Blossey et al., 2001). Of these, about 50% are regularly monitored using standardized monitoring protocols to assess the impact of the biocontrol agents on L. salicaria. Released herbivore species were established in over 10 provinces of Canada and 30 states of the USA (Blossey et al., 2001) and at several sites had selectively reduced L. salicaria biomass by 95% (Blossey et al., 2002). However, 10 years after release of the two Galerucella species in the state of New York, USA, Grevstad (2006) found no significant impacts at all on L. salicaria populations. Also, mass emergence of adults of Galerucella spp. was also found to result in localized, short-term attack on native species including Decodon verticillatus, Potentilla anserina and Rosa rugosa at some sites (Blossey et al., 2001).
 
Integrated control

Henne et al. (2005) found that an integrated vegetation management (IVM) strategy using herbicides and biological control outperformed either technique used in isolation. An integrated approach for effective, long-term management through the integration of physical, cultural, mechanical, biological and chemical control strategies was also recommended by Woo et al. (2002).

References

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22/11/2007 Updated by:

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