Salix cinerea (grey sallow)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Impact Summary
- Risk and Impact Factors
- Similarities to Other Species/Conditions
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Salix cinerea L.
Preferred Common Name
- grey sallow
Other Scientific Names
- Salix acuminata Mill.
- Salix 'AG'
- Salix aquatica Sm.
- Salix 'Aquatica'
- Salix aurita var. cinerea (L.) Fiori
International Common Names
- English: European gray willow; gray sallow; gray willow; grey willow; large gray willow; large grey willow; pussy willow; rusty sallow
- French: saule cendré
Local Common Names
- Denmark: graa pil; rust pil
- Germany: Asch Weide; Grau-Weide
- Italy: salice cenerina; salice cerognolo
- Netherlands: grauwe wilg
- Poland: wierzba szara
- Slovakia: vrba popelavá
- Slovenia: pepelnatosiva vrba
- SAXCI (Salix cinerea)
Summary of InvasivenessTop of page
S.cinerea was introduced from its native Eurasia mainly for riverbank stabilization. It is now a serious threat to riparian and wetland environments in New Zealand, southeastern Australia and increasingly in parts of the east and northeast USA, one of the most invasive of several weedy Salix spp. it can spread profusely via seed and stem fragments, one or the other noted as prevalent in different areas, forming monocultures and crowding out native vegetation, and autumn leaf-fall is thought to affect water quality.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Salicales
- Family: Salicaceae
- Genus: Salix
- Species: Salix cinerea
Notes on Taxonomy and NomenclatureTop of page
Salix is a large genus of some 300-500 species, sub-divided into several subgenera and numerous sections. Salixcinerea, known as grey sallow or large grey willow, was included by Rechinger (1964) in the section Capreae of subgenus Caprisalix, though other taxonomists have proposed different classifications, and S. cinerea is currently considered to be part of subgenus Vetrix, largely equivalent to the former Caprisalix (shrub willows, sallows and osiers) shrubbier species. Two other subgenera are subgenus Salix (tree willows) and subgenus Chamaetia (dwarf, alpine or arctic willows) (van Kraayenoord et al., 1995). Most species within each subgenera can hybridize if flowering times overlap, and there are also many hybrids, both cultivated such as S. viminalis (S. x calodendron) in its native range (McElroy et al., 1983), and spontaneous hybrids from the native range and where introduced. In Australia for example, hybridisation is being increasingly recognised as commonplace, and several ‘species’ have resulted (Cremer, 1999).
DescriptionTop of page
S. cinerea is typically a large shrub 1-2 m tall, rarely a small tree 7 (-10) m high, generally much branched from the base forming a broad, rounded crown. Bark is dark grey to dark grey-brown, smooth when young becoming fissured with age. Twigs dark reddish-brown, and densely pubescent when young, becoming glabrous when 2 years old. A distinct feature are the long ridges visible on branches when the bark is removed. Leaves very variable, not bitter to the taste, usually obovate, ovate or oblanceolate, 2-7(-9) cm long, (1-)1.5-3.5 cm wide, upper surface dull grey-green and pubescent or dark green and lustrous, covered with soft grey hairs underneath. Separate male and female catkins, each cylindrical, 15-35 mm long, appearing before leaves in March-April. Male flowers with 2 free stamens. Capsule with two valves, up to 10 mm.
DistributionTop of page
It is a Eurasian species, commonly distributed throughout Europe, from the Mediterranean to Scandinavia, and extending eastward to Asia, from Crimea to the Caucasus, from northern Iran to Siberia and north of the Caspian and Aral seas to the Chinese border (Jalas and Suominen, 1976; Skvortsov, 1999).
Distribution TableTop of page
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/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Planted||Reference||Notes|
|Azerbaijan||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|China||Present||Flora of China Editorial Committee, 2007|
|-Xinjiang||Present||Natural||Flora of China Editorial Committee, 2007|
|India||Present||Present based on regional distribution.|
|-Jammu and Kashmir||Present||Planted||CABI, 2005|
|Kazakhstan||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Turkey||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|-Nova Scotia||Present||Introduced||USDA-NRCS, 2008|
|-New Jersey||Present||Introduced||USDA-NRCS, 2008|
|-New York||Present||Introduced||USDA-NRCS, 2008|
|-North Carolina||Present||Introduced||USDA-NRCS, 2008|
|-South Carolina||Present||Introduced||USDA-NRCS, 2008|
|-West Virginia||Present||Introduced||USDA-NRCS, 2008|
|Albania||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Austria||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Belarus||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Belgium||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Bulgaria||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Czech Republic||Present||Natural||CABI, 2005|
|Czechoslovakia (former)||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Denmark||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Estonia||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Finland||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|France||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Germany||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Greece||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Hungary||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Italy||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Latvia||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Lithuania||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Moldova||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Netherlands||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Norway||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Poland||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Romania||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Russian Federation||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|-Central Russia||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|-Northern Russia||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|-Southern Russia||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|-Western Siberia||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Spain||Localised||Native||Not invasive||Natural||USDA-ARS, 2008||North-east|
|Sweden||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Switzerland||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|UK||Localised||Native||Not invasive||Natural||USDA-ARS, 2008||England|
|Ukraine||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Yugoslavia (former)||Present||Native||Not invasive||Natural||USDA-ARS, 2008|
|Australia||Localised||Introduced||Planted||USDA-ARS, 2008||Naturalized, almost entirely in the south-east|
|-New South Wales||Present||Introduced||Invasive||Royal Botanic Gardens Sydney, 2008|
|-Queensland||Present, few occurrences||Introduced||Royal Botanic Gardens Sydney, 2008|
|-South Australia||Present, few occurrences||Introduced||Royal Botanic Gardens Sydney, 2008|
|-Tasmania||Present||Introduced||Royal Botanic Gardens Sydney, 2008|
|-Victoria||Present||Introduced||Invasive||Royal Botanic Gardens Sydney, 2008|
|-Western Australia||Present, few occurrences||Introduced||Royal Botanic Gardens Sydney, 2008|
|New Zealand||Present||Introduced||1925||Invasive||Planted||Owen, 1996; Roy et al., 2005; USDA-ARS, 2008||Naturalized weed|
History of Introduction and SpreadTop of page
It was introduced to New Zealand in 1925 (Owen, 1996), and may have been introduced to Australia and North America around the same time. It had been noted as spreading along riverbanks in eastern USA in the 1990s, but it was only noticed as an invasive species in Massachusetts, USA in 2005, though was assumed to have been present for many decades (USDA Forest Service, 2006), and it is possible that it remains an unidentified invasive elsewhere in the USA or in other countries. S. cinerea is the most seriously invasive Salix species in Australia, and large and rapidly expanding populations occur in Victoria, and this species will probably become a major wetland and riverside weed as it is in New Zealand (CRC Weed Management, 2003). In Australia to date, only a few thousand kilometres of streams have been infested badly, i.e. less than 10% of potential willow habitat, and thus except for some of the S. cinerea infestations it is still possible and worthwhile to control the willows in Australia (Cremer, 2003).
Risk of IntroductionTop of page
It is listed on the New Zealand National Plant Pest Accord (Roy et al., 2005), on the the USA Mid-Atlantic EPPC list, and is declared an Australian Weed of National Significance (Thorp and Lynch, 2000) and is the most invasive Salix spp. in Australia, being invasive in New South Wales and Victoria, and potentially invasive in South Australia, Queensland and Tasmania. It could become invasive in similar climates in South America is introduced there, and all exotic Salix species should monitored for invasive behaviour wherever present.
HabitatTop of page
Willows in their native ranges occur in permanently or seasonally wet, inundated or waterlogged sites, and S. cinerea in the UK is found in fenland, carrs and occasionally in damp woods especially as sunny edges. Unlike other Salix spp., however, S. cinerea is the only one recorded to invade non-riparian habitats such as wetlands and drainage lines, and is found invading swamps, riverbanks and also wet areas behind coastal dunes. It may also become dominant in swampy areas in New Zealand (Roy et al., 2005). Harman (2004) noted that both subspecies, ssp. cinerea and, to a much lesser extent, ssp. oleifolia, are found in swamps, riverbanks, and other wet areas, and Cremer (2003) noted it as invasive in riparian habits, brackish wetlands on coastlands, wet forests, alpine bogs, disturbed and undisturbed lands.
Habitat ListTop of page
|Terrestrial ‑ Natural / Semi-natural||Riverbanks||Principal habitat||Harmful (pest or invasive)|
|Wetlands||Secondary/tolerated habitat||Harmful (pest or invasive)|
|Coastal areas||Secondary/tolerated habitat||Harmful (pest or invasive)|
|Coastal dunes||Secondary/tolerated habitat||Harmful (pest or invasive)|
Biology and EcologyTop of page
S. cinerea is able to hybridize with other members of subgenus Vetrix.
S. cinerea is a dioecious species, and both male and female flowers are highly attractive to bees, and as such considered to be commonly pollinated by insects such as the introduced European bee (Apis spp.) or native bees (Cremer, 1999) though maybe partly pollinated by wind. Flowering and the production of viable seed may begin from 2-3 years old. Ripe fruits open when dry, and the movement of cottony hairs levers seed out, accelerated by wind. Seed will germinate on and under water and tiny seedlings can survive under water for up to a month but cannot grow until exposed to air (Cremer, 2003).
S. cinerea is a temperate species and can tolerate hard and persistent frost. Being a riparian species, it can also tolerate a wide variety of rainfall regimes as long as the soil in which is grows is permanently moist or wet. S. cinerea can grow on light (sandy), medium (loamy) and heavy (clay) soils and even heavy clay soil as long as they are regularly moist or wet soil. It can tolerate permanent water logging and poor aeration, and prefers acid and neutral soils with a pH down to 3.5, making it an extremely hardy species (Cremer, 2003).
ClimateTop of page
|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)|
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Absolute minimum temperature (ºC)||>-30|
|Mean annual temperature (ºC)||0||15|
|Mean maximum temperature of hottest month (ºC)||15||23|
|Mean minimum temperature of coldest month (ºC)||-10||5|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Dry season duration||0||2||number of consecutive months with <40 mm rainfall|
|Mean annual rainfall||500||2500||mm; lower/upper limits|
Notes on Natural EnemiesTop of page
Harman (2004) includes a thorough list of insects recorded as attacking Salix spp. and S. cinerea in particular. Also, a list of 76 diseases found on Salix spp. in New Zealand is included in Harman (2004), who noted that only Melampsora epitea was specific, though it was also recorded on S. cinerea × viminalis, and S. reichardtii (pussy willow), a cross that contains S. cinerea. The self-introduced willow sawfly (Nematus oligospilus) damages many different willow species as well as poplars in New Zealand, with the host range being wider than was first anticipated (Harman, 2004). S. cinerea does not appear, however, to be suppressed by natural enemies in New Zealand, although an extensive number of invertebrates and diseases have been recorded from Salixspecies in the Northern Hemisphere. Some of these are highly damaging pests of commercially grown species such as S. viminalis, suggesting potential for reducing vigour and reproduction of S. cinerea.
Means of Movement and DispersalTop of page
Natural Dispersal (Non-Biotic)
Willows reproduce either by seed or vegetatively, typically by broken branches taking root. Both sexes of S. cinerea occur in New Zealand and reproduction is almost exclusively by seed that is capable of very wide dispersal, and the prolific production of light wind dispersed seed is probably an important factor in the invasiveness of this species (Harman, 2004). S. cinerea seed will float on water while it remains attached to its cotton parachute, though that soon falls off unless the water is very still, but it is possible for seedlings to be transported by flooding up to 100 km (Cremer, 1999, 2003). The very light seeds can travel some distance in the wind and it can thus invade areas such as cleared woodland where the soil has been disturbed. However, in Australia, spread of S. cinerea is considered to be mostly by stem sections spreading downstream (Cremer, 2003).
Long distance dispersal has been due to intentional introduction and planting, largely for riverbank erosion control, and it continues to be promoted as such.
Impact SummaryTop of page
|Environment (generally)||Positive and negative|
ImpactTop of page
In Australia, the spread of S. cinerea has negative effects on biodiversity and stream morphology via impacts on stream hydrology, stream ecology and riparian ecology, and Cremer (2003) and others have detailed the environmental imapcts. This includes impacts on: river geomorphology, river dynamics, the pool-riffle sequence, frequency of flooding, rates of bank erosion, physio-chemical properties of water, in-stream habitat quality, nutrient input, displacing native vegetation such as native Eucalyptus spp., and affecting faunal food and habitat quality. S. cinerea obstructs and diverts streamflow due to thicket establishment on banks and invasion of shallow water by branches falling into the water and rooting. S. cinerea also produce dense shade during the growing season eliminating many native terrestrial plants growing beneath and possibly decrease water temperature, and leaf-fall may reduce oxygen content.
However, in contrast to these negative impacts, willows do have a positive impact, for example, providing stream stabilisation as well as food and habitat for native animals where native vegetation is absent.
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Has a broad native range
- Abundant in its native range
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Pioneering in disturbed areas
- Highly mobile locally
- Fast growing
- Has high reproductive potential
- Reproduces asexually
- Has high genetic variability
- Ecosystem change/ habitat alteration
- Modification of hydrology
- Modification of nutrient regime
- Modification of successional patterns
- Monoculture formation
- Reduced native biodiversity
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Competition - monopolizing resources
- Competition - shading
- Rapid growth
- Difficult to identify/detect in the field
- Difficult/costly to control
UsesTop of page
All Salix spp. have been used extensively for riverbank protection and soil stabilisation, also in shelterbelts, and some have ornamental value, and apparently there are no alternative to willows for flood protection (Harman, 2004). Fresh bark of all Salix spp. contains salicin, which decomposes into salicylic acid, closely related to aspirin. Bark is removed in the summer and dried for later use, taken internally for treating rheumatism, arthritis, gout, inflammatory stages of auto-immune diseases, diarrhoea, dysentery, feverish illnesses, neuralgia and headache. Fresh or dry leaves are used internally to treat minor fevers and colic.
Similarities to Other Species/ConditionsTop of page
S. cinerea may be confused with any number of similar Salix spp., many of which may be invasive in the same areas. Striations under the bark of twigs is often given as one of better distinguishing features, though numerous keys and field guides exist. However, expert advice could be sought to positively identify the Salix species present, as spontaneous hybrids are known to occur. To further complicate an already complicated taxonomy in the introduced range, it may involve species that do not have sympatric ranges in their native range.
ReferencesTop of page
Adair R; Sagliocco JL; Bruzzese E, 2006. Strategies for the biological control of invasive willows (Salix spp.) in Australia. Australian Journal of Entomology, 45(4):259-267. http://www.blackwell-synergy.com/servlet/useragent?func=showIssues&code=aen
Christensen KI; Nielsen H, 1992. Rusty sallow (Salix cinerea subsp. oleifolia) - an overlooked sallow in Denmark and Scandinavia. [Rust-pil (Salix cinerea subsp. oleifolia) - en overset pil i Danmark og Skandinavien.] Dansk Dendrologisk Arsskrift, 10: 5-17; 13 ref.
Cremer K; Kraayenoord CV; Parker N; Streatfield S, 1995. Willows spreading by seed - implications for Australian river management. Australian Journal of Soil and Water Conservation, 8(4):18-27; 25 ref.
Forest Service USDA, 2006. From obscurity to notoriety: large gray willow. A forest health program success story. USDA Forest Service, Northeastern Area State and Private Forestry. http://www.na.fs.fed.us/ss/06/fh/gray_willow_access.pdf
Harman HM, 2004. Feasibility of biological control of grey willow Salix cinerea. DOC Science Internal Series, 183. Wellington, New Zealand: Department of Conservation, 29 pp. http://www.doc.govt.nz/upload/documents/science-and-technical/dsis183.pdf
Jalas J; Suominen J, 1976. Atlas Florae Europeae. Distribution of vascular plants in Europe. Vol. 3. Salicaceae to Balanophoraceae. Helsinki, Finland.
McElroy GH; Dawson M; Stott KG; Parfitt RI, 1983. Willows biomass as source of fuel. Long Ashton Research Station. University of Bristol, No. 83/7.
Meikle RD, 1984. Willows and poplars of Great Britain and Ireland. London, UK: BSDI.
Muyt A, 2001. Bush invaders of South-East Australia: a guide to the identification and control of environmental weeds found in South-East Australia. Meredith, Australia: R.G. and F.J. Richardson, xvi + 304 pp.
Owen SJ, 1996. Ecological weeds on conservation land in New Zealand: a database. Department of Conservation, Wellington, New Zealand: DOC Science Publications. http://www.hear.org/weedlists/other_areas/nz/nzecoweeds.htm
Rechinger KH, 1964. Salix L. In: Tutin TG, Heywood VH, Burges NA, Valentine DH, Walters SM, Webb DA, eds. Flora Europaea, Volume 1. Cambridge, UK: Cambridge University Press.
Schiechtl HM, 1996. Use of willows: Central European and Mediterranean species, their use and identification. I salici nell'uso pratico: i salici dell'Europa centrale e dell'area centrale del Mediterraneo, il loro impiego, la loro determinazione., 178 pp.; 4 pp. of ref.
Skvortsov AK, 1999. Willows of Russia and adjacent countries. Taxonomical and geographical revision. Report Series No. 39. Joensuu, Finland: Faculty of Mathematics and Natural Sciences, University of Joensuu. 307pp.
USDA-ARS, 2008. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx
ContributorsTop of page
29/02/2008 Updated by:
Nick Pasiecznik, Consultant, France
Distribution MapsTop of page
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