Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Epilobium ciliatum
(northern willowherb)



Epilobium ciliatum (northern willowherb)


  • Last modified
  • 19 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Epilobium ciliatum
  • Preferred Common Name
  • northern willowherb
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • E. ciliatum is a dicot perennial herb that is native to much of North America, southern South America and East Asia. It has been accidentally introduced into Europe, Australia and New Zealand. The distribution...

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Epilobium ciliatum (Northern or fringed willowherb); flowering plant.
TitleFlowering plant
CaptionEpilobium ciliatum (Northern or fringed willowherb); flowering plant.
Copyright©Trevor James/Hamilton, New Zealand-2014
Epilobium ciliatum (Northern or fringed willowherb); flowering plant.
Flowering plantEpilobium ciliatum (Northern or fringed willowherb); flowering plant.©Trevor James/Hamilton, New Zealand-2014
Epilobium ciliatum (Northern or fringed willowherb); young vegetative plant.
TitleYoung vegetative plant
CaptionEpilobium ciliatum (Northern or fringed willowherb); young vegetative plant.
Copyright©Trevor James/Hamilton, New Zealand-2014
Epilobium ciliatum (Northern or fringed willowherb); young vegetative plant.
Young vegetative plantEpilobium ciliatum (Northern or fringed willowherb); young vegetative plant.©Trevor James/Hamilton, New Zealand-2014
Epilobium ciliatum (Northern or fringed willowherb); flower.
CaptionEpilobium ciliatum (Northern or fringed willowherb); flower.
Copyright©Trevor James/Hamilton, New Zealand-2014
Epilobium ciliatum (Northern or fringed willowherb); flower.
FlowerEpilobium ciliatum (Northern or fringed willowherb); flower.©Trevor James/Hamilton, New Zealand-2014
Epilobium ciliatum (Northern or fringed willowherb); open fruiting capsule, showing seeds with attached hairs.
TitleOpen fruiting capsule
CaptionEpilobium ciliatum (Northern or fringed willowherb); open fruiting capsule, showing seeds with attached hairs.
Copyright©Trevor James/Hamilton, New Zealand-2014
Epilobium ciliatum (Northern or fringed willowherb); open fruiting capsule, showing seeds with attached hairs.
Open fruiting capsuleEpilobium ciliatum (Northern or fringed willowherb); open fruiting capsule, showing seeds with attached hairs.©Trevor James/Hamilton, New Zealand-2014


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Preferred Scientific Name

  • Epilobium ciliatum Raf.

Preferred Common Name

  • northern willowherb

Other Scientific Names

  • Chamaenerion dominii Nábelek
  • Epilobium aconcaguinum Phil.
  • Epilobium adenocaulon Hausskn.
  • Epilobium adenocladon Rydb.
  • Epilobium affine Maxim.
  • Epilobium alaskae H.Lév.
  • Epilobium cunninghamii Hausskn.
  • Epilobium fendleri Hausskn.
  • Epilobium parishii Trel.
  • Epilobium perplexans (Trel.) Trel. ex A.Nelson
  • Epilobium praecox Suksd.
  • Epilobium pseudolineare Hausskn.
  • Epilobium punctatum H.Lév.
  • Epilobium rubescens Rydb.
  • Epilobium santa-cruzense Dusén
  • Epilobium ursinum C.S.P.Parish ex Trel.
  • Epilobium valdiviense Hausskn.

International Common Names

  • English: american willowherb; fringed willowherb; glandular willowherb; hairy willowherb; hairy willowweed
  • Spanish: epibolio ciliado
  • French: epilobe cilié

Local Common Names

  • Czech Republic: vrbovka zl znat 
  • Denmark: hvid dueurt; kirtel-dueurt
  • Estonia: metspajulill; punakas pajulill
  • Finland: amerikanhorsma; vaalea-amerikanhorsma
  • Germany: Bewimpertes Weidenroschen; Drüsiges Weidenröschen
  • Italy: garofanino ciliato
  • Latvia: laukuotastiebe ozkaroze
  • Lithuania: dziedzerstublaja kazroze
  • Netherlands: gewimperde basterdwederik
  • Poland: wierzbownica gruczolowata
  • Sweden: amerikansk dunört

Summary of Invasiveness

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E. ciliatum is a dicot perennial herb that is native to much of North America, southern South America and East Asia. It has been accidentally introduced into Europe, Australia and New Zealand. The distribution of this species is increasing as it rapidly spreads over Britain and many other European countries. It produces copious wind-borne seed and can, under favourable conditions, complete its life cycle from seed to seed in as little as nine to ten weeks. E. ciliatum has been described as an aggressive species and can become a noxious weed, particularly in agricultural areas. Even in its native range in North America it has proved to be a problem in agricultural land, in orchards and vineyards and in container plants in nurseries. Due to its rapid growth E. ciliatum can outcompete and displace native plant species. It is also possible for it to hybridize with native Epilobium species. Control of E. ciliatum is difficult to achieve due to herbicide resistance and tolerance.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Myrtales
  •                         Family: Onagraceae
  •                             Genus: Epilobium
  •                                 Species: Epilobium ciliatum

Notes on Taxonomy and Nomenclature

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The genus Epilobium contains around 165 species found in temperate zones, the majority from West North America and also on arctic and tropical mountains (Mabberley, 1997). A total of 79 synonyms of this species are listed on The Plant list (2013).

Stace (2010), in his entry for E. ciliatum, points out that some taxonomists claim that the species E. adenocaulon ‘is distinct, but this name seems predated by E. watsonii Barbey’. According to ITIS (2014)E. adenocaulon is an early synonym for E. ciliatum subsp. ciliatum and E. watsonii [E. ciliatum subsp. watsonii] is a recognized subspecies of E. ciliatum.

ITIS (2014) list three subspecies of E. ciliatum. These include; E. ciliatum subsp. ciliatum Raf.; E. ciliatum subsp. glandulosum (Lehm.) Hoch & P.H. Raven and E.ciliatum subsp. watsonii (Barbey) Hoch & P.H. Raven. All three subspecies have previously been referred to other taxa and are now considered synonyms (ITIS, 2014). The native distribution of the subspecies ciliatum ranges throughout North America, East Asia and southern South America. The subspecies glandulosum occurs in northern and eastern North America and the subspecies watsonii along the west coast from California to British Columbia (USDA-NRCS, 2014).


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E. ciliatum is a perennial herb, erect, more or loosely clumped, with basal rosettes or fleshy shoot, generally strigose in lines, glandular distally, occasionally spreading-hairy. Leaf, 1–12 cm, narrowly lanceolate to ovate, fine-toothed; veins conspicuous; petiole 0–5(8) mm. Inflorescence: densely strigose, ± spreading-hairy, generally glandular. Flower, hypanthium 0.5–2.6 mm; sepals 2–7.5 mm; petals white to rose-purple; stamens <= pistil; stigma club- or head-like. Fruit: 15–100 mm, hairy; pedicel 0–15(40) mm. Seed, 0.8–1.6 mm, ridged, hair-tuft deciduous (Jepson Flora Project, 2014).

Plant Type

Top of page Broadleaved
Seed propagated


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E. ciliatum is native to southern parts of Canada and much of the USA, South America and East Asia. It is however listed as an endangered species in the states of Indiana and Maryland, threatened in New Hampshire and of special concern (low population numbers and restricted range) in Tennessee (USDA-NRCS, 2015).

E. ciliatum has been introduced into parts of Europe, Australia and New Zealand where it is spreading rapidly.

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


ChinaPresentPresent based on regional distribution.
-HeilongjiangPresentNativeUSDA-ARS, 2014
-JilinPresentNativeUSDA-ARS, 2014
JapanPresentPresent based on regional distribution.
-HokkaidoPresentNativeUSDA-ARS, 2014
-HonshuPresentNativeUSDA-ARS, 2014
Korea, Republic ofPresentNativeUSDA-ARS, 2014

North America

CanadaPresentPresent based on regional distribution.
-AlbertaPresentNativeUSDA-NRCS, 2014
-British ColumbiaPresentNativeUSDA-NRCS, 2014
-ManitobaPresentNativeUSDA-NRCS, 2014
-Northwest TerritoriesPresentNativeUSDA-NRCS, 2014
-OntarioPresentNativeUSDA-NRCS, 2014
-SaskatchewanPresentNativeUSDA-NRCS, 2014
GreenlandPresentNativeUSDA-NRCS, 2014
MexicoPresentNativeUSDA-NRCS, 2014
Saint Pierre and MiquelonPresentNativeUSDA-NRCS, 2014
USAPresentPresent based on regional distribution.
-AlabamaPresentNativeUSDA-NRCS, 2014
-AlaskaPresentNativeUSDA-NRCS, 2014
-CaliforniaWidespreadNative Invasive USDA-NRCS, 2014
-ColoradoPresentNativeUSDA-NRCS, 2014
-ConnecticutPresentNativeUSDA-NRCS, 2014
-DelawarePresentNativeUSDA-NRCS, 2014
-District of ColumbiaPresentNativeUSDA-NRCS, 2014
-FloridaPresentNativeUSDA-NRCS, 2014
-GeorgiaPresentNativeUSDA-NRCS, 2014
-IdahoPresentNativeUSDA-NRCS, 2014
-IllinoisPresentNativeUSDA-NRCS, 2014
-IndianaPresentNativeUSDA-NRCS, 2014
-IowaPresentNativeUSDA-NRCS, 2014
-KansasPresentNativeUSDA-NRCS, 2014
-KentuckyPresentNativeUSDA-NRCS, 2014
-LouisianaPresentNativeUSDA-NRCS, 2014
-MainePresentNativeUSDA-NRCS, 2014
-MarylandPresentNativeUSDA-NRCS, 2014
-MassachusettsPresentNativeUSDA-NRCS, 2014
-MichiganPresentNativeUSDA-NRCS, 2014
-MinnesotaPresentNativeUSDA-NRCS, 2014
-MississippiPresentNativeUSDA-NRCS, 2014
-MissouriPresentNativeUSDA-NRCS, 2014
-MontanaPresentNativeUSDA-NRCS, 2014
-NebraskaPresentNativeUSDA-NRCS, 2014
-NevadaPresentNativeUSDA-NRCS, 2014
-New MexicoPresentNativeUSDA-NRCS, 2014
-New YorkPresentNativeUSDA-NRCS, 2014
-North CarolinaPresentNativeUSDA-NRCS, 2014
-North DakotaPresentNativeUSDA-NRCS, 2014
-OhioPresentNativeUSDA-NRCS, 2014
-OklahomaPresentNativeUSDA-NRCS, 2014
-OregonPresentNativeUSDA-NRCS, 2014
-PennsylvaniaPresentNativeUSDA-NRCS, 2014
-Rhode IslandPresentNativeUSDA-NRCS, 2014
-South CarolinaPresentNativeUSDA-NRCS, 2014
-South DakotaPresentNativeUSDA-NRCS, 2014
-TennesseePresentNativeUSDA-NRCS, 2014
-TexasPresentNativeUSDA-NRCS, 2014
-UtahPresentNativeUSDA-NRCS, 2014
-VermontPresentNativeUSDA-NRCS, 2014
-VirginiaPresentNativeUSDA-NRCS, 2014
-WashingtonPresentNativeUSDA-NRCS, 2014
-West VirginiaPresentNativeUSDA-NRCS, 2014
-WisconsinPresentNativeUSDA-NRCS, 2014
-WyomingPresentNativeUSDA-NRCS, 2014

Central America and Caribbean

GuatemalaPresentNativeUSDA-ARS, 2014

South America

ArgentinaPresentNativeUSDA-ARS, 2014Chubut, Cordoba, Mendoza, Neuquen, Rio Negro, San Juan, San Luis, Santa Cruz, Tierra del Fuego
ChilePresentNativeUSDA-ARS, 2014


AustriaPresentIntroducedDAISIE, 2015
BelgiumWidespreadIntroduced Invasive Invasive Species in Belgium, 2014
CroatiaPresentIntroduced Invasive Krajsek and Jogan, 2004
Czech RepublicPresentIntroduced Invasive Williamson et al., 2005
DenmarkPresentIntroducedDAISIE, 2015
EstoniaPresentIntroducedDAISIE, 2015
Faroe IslandsPresentIntroducedDAISIE, 2015
FrancePresentIntroducedDAISIE, 2015
GermanyPresentIntroducedDAISIE, 2015
HungaryPresentIntroducedDAISIE, 2015
IrelandPresentIntroduced Invasive Doogue et al., 1985
ItalyPresentIntroducedDAISIE, 2015
LithuaniaWidespreadIntroduced Invasive Matulevičiūtė, 2007
LuxembourgPresentIntroducedDAISIE, 2015
NetherlandsPresentIntroducedDAISIE, 2015
NorwayPresentIntroducedDAISIE, 2015
PolandPresentIntroducedDAISIE, 2015
RomaniaPresentIntroducedDAISIE, 2015Not established
SloveniaPresentIntroduced Invasive Krajsek and Jogan, 2004
SpainPresentIntroduced Invasive Fernández Alonso, 2012
SwedenPresentNativeDAISIE, 2015
SwitzerlandPresentIntroduced Invasive Invasive Alien Species in Switzerland, 2006Present in the Jura and Plateau and its distribution is expanding
UKWidespreadIntroduced Invasive Stace, 2010Still spreading
-Channel IslandsPresentIntroducedDAISIE, 2015
-Northern IrelandPresentIntroducedDAISIE, 2015
UkrainePresentIntroducedDAISIE, 2015


AustraliaPresentIntroducedUSDA-ARS, 2014
-New South WalesPresentIntroducedCouncil of Heads of Australasian Herbaria, 2014
-QueenslandPresentIntroducedCouncil of Heads of Australasian Herbaria, 2014
-South AustraliaPresentIntroducedCouncil of Heads of Australasian Herbaria, 2014
-TasmaniaPresentIntroduced1919Council of Heads of Australasian Herbaria, 2014
-VictoriaPresentIntroduced1969Council of Heads of Australasian Herbaria, 2014
-Western AustraliaPresentIntroduced1974Council of Heads of Australasian Herbaria, 2014
New ZealandWidespreadIntroduced Invasive Webb et al., 1988

History of Introduction and Spread

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Stace (2010) reports that E. ciliatum was first recorded in Britain in 1891 and that its distribution is increasing over most of the British Isles. Preston (1988) speculated that it may have been introduction to Britain in or on timber, on the strength of two of its first three localities in Britain being timber yards. A detailed account of its spread, from its first record in Leicestershire in 1891, where it occurred initially among several other species of the same genus on the muddy shores left dry by the receding waters of a reservoir, is provided by Preston (1988). This species spread dramatically through Britain and reached Dorset and then Wales in 1942. From then on the rate of spread accelerated and by 1969 it was common throughout most of south-east England (Preston, 1988). Invasive Alien Species of Switzerland (2006) suggest that the species has been moved in soil and attached to animals, vehicles, etc., since its first arrival in Britain.

It was suggested that the presence of E. ciliatum in New Zealand may have result from introductions from Britain, but the authors mischievously speculate that the ‘possibility that it was introduced from New Zealand to Britain, rather than vice versa, cannot be ruled out’ (Raven and Raven, 1976). Given that the species occurs as a ‘wool alien’ in Britain certainly means that this could be true (Shimwell, 2006). 


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Czech Republic 1960 Yes Williamson et al. (2005) Accidential
Lithuania 1926 Yes Matulevičiūtė (2007) Accidential
Scotland 1957 Yes Invasive alien species in Switzerland (2006) Accidential
Tasmania 1919 Yes Council of Heads of Australasian Herbaria (2014)
UK 1891 Yes Preston (1988) Accidential

Risk of Introduction

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There is little doubt that A. ciliatum will continue to spread across land borders into other European countries to which the large number of seeds could be carried by the wind, on the tyres of vehicles or in their slipstream. Its spread will also continue within those countries where its distribution is at present limited or patchy.


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In its native range of California, USA, E. ciliatum is found throughout the state up to 4100 m in altitude, in moist or dry disturbed areas. This includes meadows and wetlands, agricultural areas, wet and moist sites, streambanks, ditches, irrigation canals as well as in orchards, nurseries, vineyards and landscaped areas (UCIPM, 2014). It has been suggested that in North America it occupies a range of soil types, occurring on light or heavy, calcareous or non-calcareous soils (Wiegand and Eames, 1926). On Vancouver Island and southern British Columbia it occurs in disturbed areas, roadsides, fields and ditches (Klinkenberg, 2014). Similarly in China it grows in moist, disturbed places along streams, rivers, roadside ditches, slopes and seeps (Flora of China Editorial Committee, 2014).

In Britain, to which it was introduced many years ago, E. ciliatum has spread into woodlands and many man-made or modified habitats such as railway banks, roadsides, river-banks, gardens and plant nurseries (Myerscough and Whitehead, 1966; Stace, 2010). In Lithuania, Matuleviciute (2007), found that plants were most frequently found in areas occupied by wet natural and semi-natural open wet habitats, often on the banks of waterways or in periodically flooded habitats. In Lithuania, as elsewhere, E. ciliatum prefers well-lit, moist, mesotrophic or eutrophic habitats with low acid to neutral soil reaction (Matuleviciute and Sprainaityte, 2010). However, in Slovenia and Croatia it is found in dry meadows and shrubland (Krajsek and Jogan, 2004). Havaux (1990) commented that E. ciliatum was very common in Northern France and Belgium, where it grows rapidly on poor and marginal lands and added that its high competitiveness was presumably due to its tolerance of unfavourable growth conditions, especially the very low light conditions needed for growth (Havaux, 1990).

In New Zealand, according to Webb et al. (1988) it is similarly found on waste land, especially where moist, in and around swamps, river beds and ponds and in cultivated soil. 

Habitat List

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Terrestrial – ManagedCultivated / agricultural land Present, no further details Natural
Protected agriculture (e.g. glasshouse production) Present, no further details Natural
Managed forests, plantations and orchards Present, no further details Natural
Rail / roadsides Present, no further details Natural
Urban / peri-urban areas Present, no further details Natural
Terrestrial ‑ Natural / Semi-naturalRiverbanks Present, no further details Natural

Biology and Ecology

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The Jepson Flora Project (2014) has reported a diploid number of 2n=36 for E. ciliatum.

A number of hybrids of E. ciliatum with other Epilobium species have been reported. Seavey (1993) found that E. ciliatum can successfully hybridize with E. luteum producing fertile hybrids. He also found field-collected plants of E. treleasianum from the Olympic Mountains in Washington State that were clearly the result of natural hybridization between E. ciliatum subsp. glandulosum and E. luteum (Seavey, 1993). Kitchener and McKean (1998) also reported that in New Zealand E. ciliatum had hybridized with the native E. brunnescens. Such hybrids were first reported in Britain in 1995 (Kitchener and McKean, 1998) and were formally recognised as E. x brunnatum. Since E. ciliatum is still spreading rapidly in Britain, Kitchener and McKean (1988) speculate that hybrids are likely to become more common in future.

Reproductive Biology

In California E. ciliatum flowers between June and September (UCIPM, 2014) and a single plant can produce up to 60,000 seeds in a season (Altland and Cramer, 2006; Altland, 2007). The seeds are small and light, weighing just 0.062 mg, with a rate of fall in still air of 16 cm sec-1 (Myerscough and Whitehead, 1966). Seeds of E. ciliatum can germinate under a relatively wide range of temperatures and light. This means that germination can occur throughout the spring and summer growing seasons in northern climates and virtually year-round in protected container crops. Altland and Cramer (2006) observed that the seeds are capable of germination in much drier soil that other species in the same genus, a conclusion also reached by Myerscough and Whitehead (1966). Seeds can germinate in full sun or partial shade at 84% of full sun and they can germinate at temperatures from 4-36°C although germination is reduced as temperatures approaching 30°C (Altland and Cramer, 2006Altland, 2007). Germination of ripe seed from recently opened seed pods occurred within four days of sowing in full sun and in less than seven days in partial shade (Altland and Cramer, 2006Altland, 2014). Seeds exposed to a pH of 3.0 did not germinate, even after subsequent transfer to pH 5.0 and those in a pH 4.0 solution had their germination reduced to less than 50%. Those seeds in solutions at pH 5.0, 4.5 or 4.0 germinated quickly and almost completely (Myerscough and Whitehead, 1966).

Plants can flower in five to six weeks from germination and then produce mature seed four weeks later. E. ciliatum therefore needs only about nine to ten weeks for plants to germinate, mature and produce another generation of seeds, allowing several generations in a single growing season.

E. ciliatum is self-pollinating and is visited by relatively few insects (small halictid bees and a species of Bombus) (Parket et al., 1995). A study looking at the reproductive allocation and fitness consequences of selfing can be found in Parket et al. (1995).

Physiology and Phenology

In England, Myerscough and Whitehead (1966) reported that the initial growth form of the seedlings depends on day length. Seedlings established in the autumn form rosettes, but those established in early summer form an elongated shoot system from the start of growth. In the latter case flower buds are formed after the production of the first four or five pairs of opposite leaves, about four to five weeks after germination. At this stage side shoots are produced and these also elongate and flower. Flowering occurs about 38 days after germination. Ripe capsules burst and shed seed about four weeks after the flowers open. Winter rosettes produced from the compact buds in the axils of cotyledons and lower leaves remain unchanged in late spring, but the terminal buds of the main axis and side shoots elongate into long internodes and flower and fruit in the same way as early summer established seedlings (Myerscough and Whitehead, 1966).

E. ciliatum shows strong apical dominance, with the main shoot suppressing the growth of lateral branches, so long as the growing point remains intact (Irwin and Aassen, 1996). Clipping the apex results in a reduction in plant height, but stimulates branched stem numbers and thus increases total branch length (Irwin and Aassen, 1996). However it was concluded that increases in nutrient level decreased the strength of apical dominance. The benefits of apical dominance were most evident for competing plants grown under high nutrient conditions where competition for light is expected to be most intense (Irwin and Aassen, 1996). Havaux (1990) suggested that the ability of E. ciliatum to grow under extreme shade conditions may be explained, at least partly, by its preservation of high oxygen yield at low photon flux densities.

According to Altland and Cramer (2006) the species can also form turions on its roots, which may also be another means of reproduction. However, in contrast to this it has been suggested that E. ciliatum subsp. ciliatum does not ‘produce underground winter buds (turions)’, but rather that E. ciliatum subsp. glandulosum is characterised by its underground turions (Minnesota Seasons, 2014


There is some conflict with regards to the longevity of the seeds. Florabase (2014) says that the seedbanks of E. ciliatum are short-lived, possibly days to one year. Myerscough and Whitehead (1966) however, state that the seeds last for several years in both laboratory and natural conditions. The plants themselves are perennials, but probably short-lived ones, forming rosettes as over-wintering structures.

Population Size and Structure

Estimated doubling times of E. ciliatum in terms of area occupied were 2.25 years in the Czech Republic and 4.67 years in Britain and Ireland (Williamson et al., 2005). However, the authors said their overall results ‘produced rather few clear explanations’ but suggested that economic and landscape factors are important in determining the rate of spread (Williamson et al., 2005).


In Lithuania, E. ciliatum most frequently occurs in plant communities belonging to the Molinio-Arrhenanthereta, Phragmito-Magnocaticetea and Isoeto-Nanojuncetea classes and communities of wetter habitats (Matuleviciute, 2007). Its most common associates are Phragmites australis, Carex gracilis [C. mucronata], C. paniculata, Phalaris arundinacea and Glyceria maxima.

Environmental Requirements

A study by Myerscough and Whitehead (1967) looked at the impact of reducing nutrient availability on E. ciliatum and found that the size and degree of development of the plants was affected. E. ciliatum is well adapted to growth under shady conditions and produces larger leaves to compensate (Myerscough and Whitehead, 1967). However growth with just 10% light levels significantly decreased the dry weigh of plants when compared with 100%, 70% and 43% light levels (Myerscough and Whitehead, 1967).


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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)

Means of Movement and Dispersal

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Natural Dispersal

The seeds of E. ciliatum are very light and attached to a tuft of hair which aids in wind dispersal. In Oregon this occurs from June to September (Altland and Cramer, 2006). Compact buds also develop in the axils of the cotyledons and lower leaves. These are readily detached and could provide a mechanism for local spread.

Vector Transmission

The seeds may become attached to the wheels of vehicles or even blown along in their slipstreams (Preston, 1988).

Accidental Introduction

The seeds are very small and light and could easily be accidentally carried in baggage or on clothing.

Intentional Introduction

Intentional introduction of E. ciliatum is unlikely as the plants are neither showy nor have a widespread reputation as medicinal plants outside their native range.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Disturbance Yes
Hitchhiker Yes Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Plants or parts of plants Yes Yes
Wind Yes

Impact Summary

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Environment (generally) Negative

Economic Impact

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In Oregon, USA, its native range, E. ciliatum has been described as ‘one of the most difficult weeds to control in container crops and is among the top five weed species in Oregon nurseries’ (Altland and Cramer, 2006).

In Western Australia, where it was introduced, it is a common weed of nurseries and orchards (FloraBase, 2014). In Belgium it occurs as a weed in tree nurseries, fruit plantations, maize and sites of total vegetation control (Bulcke et al., 1987). As a result there is some economic impact associated with controlling this species in both its introduced and native range however no data detailing this is available.

Environmental Impact

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In countries to which it has been introduced, it is mostly a problem in man-made habitats but can also invade woodlands, damp marshland and the margins of rivers and ponds. Here it may play a crucial part in displacing native vegetation. Its rapid growth allows it to outcompete many smaller container shrubs and herbaceous perennials. A study by Willoughby et al. (2006) found that E. ciliatum is likely to affect the early growth of young tree plants such as Betula pendula by decreasing both height and diameter increment of plants.

Although rare, it is possible for E. ciliatum to form hybrids with several different Epilobium species (Invasive Species in Belgium, 2015). This may cause rare Epilobium species to suffer as a result of outbreeding (Invasive Species in Belgium, 2015).

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Pioneering in disturbed areas
  • Tolerant of shade
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Fast growing
  • Has high reproductive potential
  • Gregarious
  • Has propagules that can remain viable for more than one year
  • Has high genetic variability
Impact mechanisms
  • Competition - shading
  • Interaction with other invasive species
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control


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Social Benefit

According to Moerman (2014), E. ciliatum subsp. ciliatum is used by some native North Americans to treat leg pain where it is applied as a lotion and poultice of roots to muscular cramps. An infusion of roots of E. ciliatum is also used to treat diarrhoea.

Uses List

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Medicinal, pharmaceutical

  • Source of medicine/pharmaceutical

Similarities to Other Species/Conditions

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E. ciliatum is similar in appearance to a number of different species within the genus Epilobium. In Minnesota, E. ciliatum is often confused with E. coloratum, E. leptophyllum and E. strictum (Minnesota Seasons, 2014). These can be distinguished from each other by morphological characteristics. E. coloratum has stems and leaves often tinted purple, leaf margins more densely toothed and with shorter fruit. E. leptophyllum has narrower leaves, leaf margins not toothed but rolled back towards the underside and the upper leaf surface is covered in straight, stiff, sharp appressed hairs. E. strictum has an unbranched stem or has just a few branches. The upper and middle stem leaves are obviously alternate, leaves are narrower and are not toothed and are rolled backwards towards the underside and the upper leaf surface is densely covered in straight, spreading or ascending hairs.

E. ciliatum may also be confused with E. brachycarpum. Key differences can be found in UCIPM (2014).

In Switzerland, E. ciliatum is mostly likely to be confused with E. obscurum but the former has larger stems, is glandular on top and has white flowers (Invasive Alien Species in Switzerland, 2006).

Prevention and Control

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Cultural Control and Sanitary Measures

A study in Poland by Przepiorkowski and Gorski (1994) examined the effects of residues of rye (Secale cereale) on both triazine-resistant and triazine-susceptible Epilobium species (species not specified). They found that soil containing rye root residues inhibited germination of Epilobium seeds by up to 50% with the highest rate of rye applied. Aqueous extracts of rye shoot tissue were also found to inhibit germination, even at low concentrations (Przepiorkowski and Gorski, 1994). Planting seedlings of Epilobium species into soils containing rye roots left after the tops had been severed also resulted in lower dry weights after six weeks of growth. Thus interspersing rye into crop rotations, as is often done (Przepiorkowski and Gorski, 1994), could perhaps be used to limit the growth of populations of species of Epilobium.

Physical/Mechanical Control

Recommendations in Western Australia suggest that plants should be prevented from seeding and that small or isolated infestations of seedlings should be removed by hand. If larger plants are removed it is important not to leave any fragments of the crown behind as they may regrow (FloraBase, 2014).

Le Fer and Parker (2005), evaluated the effects of prescribed burns at different times of the year on chaparral species, of which E. ciliatum is one. They heated seeds of 13 species moist and dry to determine the moisture effect on heated seeds. Of the species tested E. ciliatum was the most tolerant of heat when dry with germination only dropping significantly at 110oC. However under moist conditions germination of the seeds of this species were significantly reduced at 70oC. As a result it was suggested that spring burns, when soil moisture is high, is probably more damaging to the natural vegetation than dry season burns (Le Fer and Parker, 2005). This helps to maintain historical fire regimes and thus decrease alterations to the ecosystem’s dynamics.

Chemical Control

Chemical control of E. ciliatum is tricky as it is resistant to a number of herbicides. For example, Heap (2015) reported resistance to atrazine and simazine in Belgium in 1980, to paraquat in Belgium in 1982, to atrazine in Poland in 1995 and to simazine and paraquat in the UK in 1981 and 1989 respectively. It has been suggested that seedlings could be sprayed with glyphosate. However older, mature plant can tolerate glyphosate and established plants will often re-sprout after treatment (FloraBase, 2014). However, Altland and Cramer (2006) tested the effects of a range of granular and liquid herbicide formulations on the pre-emergent control of E. ciliatum. Of the granular formulations, oxadiazon, oxyfluorfen plus pendimethalin and oxydiazon plus prodiamine all reduced numbers of E. ciliatum three weeks after treatment. After eight weeks, the greatest reductions in shoot dry matter were given by oxadiazon, oxydiazon plus prodiamine, oxyfluorfen plus oryzalin and flumioxazin. This treatment was found to be effective for control E. ciliatum in container plants in nurseries, however it is not known whether this method would be suitable in more natural environments.


It has been suggested that herbicides alone will not provide effective control of E. ciliatum and that a combination of good hygiene and herbicide management is required (FloraBase, 2014). Altland and Cramer (2006) suggested that control should involve using a combination of hand pulling or post-emergent applications of glyphosate.


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Altland J, 2007. Northern willowherb control in nursery containers. Oregon, USA: Oregon State University.

Altland J, 2014. Northern-willowherb management. Oregon, USA: Oregon State University.

Atland J; Cramer E, 2006. Control of northern willowherb in nursery containers. Journal of Environmental Horticulture, 24(3):143-148.

Bulcke R; Verstraete F; Himme Mvan; Stryckers J, 1987. Biology and control of Epilobium ciliatum Rafin. (syn.: E. adenocaulon Hausskn.). In: Proceedings of a meeting of the EC Experts' Group, Dublin, 12-14 June 1985. Rotterdam, A.A. Blakema, Netherlands 57-67.

Council of Heads of Australasian Herbaria, 2014. Australia's virtual herbarium, Australia.

DAISIE, 2015. Delivering Alien Invasive Species Inventories for Europe. European Invasive Alien Species Gateway.

Doogue D; Kelly DL; Wyse Jackson PS, 1985. The progress of Epilobium ciliatum Rafin. (E. adenocaulon Hausskn.) in Ireland, with some notes on its hybrids. The Irish Naturalists' Journal, 21(10):444-446.

Fernández Alonso JL, 2012. Epilobium ciliatum Rafin. (Onagraceae), a new adventive species potentially invasive in the Iberian Peninsula. (Epilobium ciliatum Rafin. (Onagraceae), una nueva adventicia potencialmente invasora en la Peninsula Ibérica.) Acta Botanica Malacitana, 37:179-184.

Flora of China Editorial Committee, 2014. Flora of China. St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria.

Florabase, 2014. Flora of Western Australia. Perth, Western Australia: Department of Environment and Conservation. http://florabase.dpaw

Havaux M, 1990. Photoacoustic study of the photochemical energy conversion in Epilobium plants grown under very low light conditions. Environmental and Experimental Botany, 30(1):101-109.

Heap I, 2015. The international survey of herbicide resistant weeds.

Invasive Alien Species in Switzerland, 2006. Inventory of alien species and their threat to biodiversity and economy in Switzerland. Bern, Switzerland: Federal Office for the Environment FOEN.,lnp6I0NTU042l2Z6ln1ad1IZn4Z2qZpnO2Yuq2Z6gpJCGdnt4hGym162dpYbUzd,Gpd6emK2Oz9aGodetmqaN19XI2IdvoaCVZ,s-.pdf

Invasive Species in Belgium, 2014. Invasive species in Belgium. Belgium: Belgian Biodiversity Platform.

Irwin DL; Aarssen LW, 1996. Effects of nutrient level on cost and benefit of apical dominance in Epilobium ciliatum. American Midland Naturalist, 136(1):14-28.

ITIS, 2014. Integrated Taxonomic Information System.

Jauzein P, 1988. [English title not available]. (Quelque adventices méconnues de la flore française.) Annales ANPP (Association Nationale Pommes Poires), 3. 199-208.

Jepson Flora Poject, 2014. Jepson eFlora. Berkeley California, USA: Univeristy of California.

Kitchener GD; McKean DR, 1998. Hybrids of Epilobium brunnescens (Cockayne) Raven & Engelhorn (Onagraceae) and their occurrence in the British Isles. Watsonia, 22(1):49-60.

Klinkenberg B, 2014. Electronic Atlas of the Plants of British Columbia. E-Flora BC. Vancouver, British Columbia, Canada: Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia.

Krajsek SS; Jogan N, 2004. Epilobium ciliatum Raf., a new plant invader in Slovenia and Croatia. Acta Botanica Croatica, 63(1):49-58.

Le Fer D; Parker VT, 2005. The effect of seasonality of burn on seed germination in chaparral: the role of soil moisture. Madroño, 52(3):166-174.

Mabberley DJ, 1997. The plant-book: a portable dictionary of the vascular plants. Ed. 2: xvi + 858 pp. Cambridge, UK: Cambridge University Press

Matuleviciute D, 2007. Peculiarities of distribution and naturalisation of Epilobium ciliatum Raf. in Lithuania. Acta Biologica Universitatis Daugavpiliensis, 7(2):113-119.

Matuleviciute D; Sprainaityte S, 2010. Population dynamics of Epilobium ciliatum in fire places in Kamanos raised bog: 5-year study (2004-2008). Acta Biologica Universitutis Dauguvpiliereslis, 2:29-35.

Minnesota Seasons, 2014. American willowherb: (Epilobium ciliatum ssp. ciliatum). Minnesota, USA.

Moerman D, 2014. Native American ethnobotany. Dearborn, Michigan, USA: University of Michigan-Dearborn.

Myerscough PJ; Whitehead FH, 1966. Comparative biology of Tussilago farfara L., Chamaenerion angustifolium (L) Scop., Epilobium montanum L. and Epilobium adenocaulon Hausskn. 1. General biology and germination. New Phytologist, 65(2):192-210.

Myerscough PJ; Whitehead FH, 1967. Comparative biology of Tussilago farfara L., Cham-aenerîon angustifolium (L.) Scop., Epilobium mon-tanum L., and Epilobium adenocaulon Hausskn. 2. Growth and ecology. New Phytologist, 66(4):785-823.

Parker IM; Nakamura RR; Schemske DW, 1995. Reproductive allocation and the fitness consequences of selfing in two sympatric species of Epilobium (Onagraceae) with contrasting mating systems. American Journal of Botany, 82(8):1007-1016.

Preston CD, 1988. The spread of Epilobium ciliatum Raf in the British Isles. Watsonia, 17(3):279-288.

Przepiorkowski T; Gorski SF, 1994. Influence of rye (Secale cereale) plant residues on germination and growth of three triazine-resistant and susceptible weeds. Weed Technology, 8(4):744-747.

Raven PH; Raven TE, 1976. The genus Epilobium in Australasia. New Zealand DSIR Bulletin 216.

Seavey SR, 1993. Natural and artificial hybrids involving Epilobium luteum (Onagraceae). Systematic Botany, 18(2):218-228.

Shimwell DW, 2006. A shoddy tale: perspectives on the wool alien flora of West Yorkshire in the twenty-first century. Watsonia, 26(2):127-137.

Stace C, 2010. New flora of the British Isles. Cambridge, UK: Cambridge University Press, 1232 pp.

The Plant List, 2013. The Plant List: a working list of all plant species. Version 1.1. London, UK: Royal Botanic Gardens, Kew.

UCIPM, 2014. Willowherbs (Epilobium ciliatum, E. brachycarpum). California, USA: University of California Agriculture and Natural Resources.

USDA-ARS, 2014. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory.

USDA-NRCS, 2014. The PLANTS Database. Baton Rouge, USA: National Plant Data Center.

Walker KJ, 2007. The last thirty five years: recent changes in the flora of the British Isles. Watsonia, 26(3):291-302.

Webb CJ; Sykes WR; Garnock-Jones PJ, 1988. Flora of New Zealand, Volume IV: Naturalised pteridophytes, gymnosperms, dicotyledons. Christchurch, New Zealand: Botany Division, DSIR, 1365 pp.

Wiegand KM; Eames AJ, 1926. The flora of the Cayuga Lake Basin, New York: vascular plants. New York, USA: Cornell University.

Williamson M; Pysek P; Jarosík V; Prach K, 2005. On the rates and patterns of spread of alien plants in the Czech Republic, Britain, and Ireland. Écoscience, 12(3):424-433.

Willoughby I; Clay DV; Dixon FL; Morgan GW, 2006. The effect of competition from different weed species on the growth of Betula pendula seedlings. Canadian Journal of Forest Research, 36(8):1900-1912.

Links to Websites

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GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway source for updated system data added to species habitat list.
Global register of Introduced and Invasive species (GRIIS) source for updated system data added to species habitat list.


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04/08/2014 Original text by:

Ian Popay, Landcare Research, New Zealand

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