Willows

Salix species

Salix alba var. vitellina (White Willow or Golden Willow)
Salix alba var. alba (White Willow)
Salix babylonica L. (Weeping Willow) is the main species in WA.
Salix cinerea L. (Common Sallow)
Salix cinerea ssp. cinerea (Grey Sallow)
Salix cinerea ssp. oleifolia (Rusty Sallow)
Salix fragilis var. fragilis (Crack Willow)
Salix matsudana hybrids (New Zealand Willow or Tortured Willow)
Salix nigra Marshall (Black Willow)
Salix x calodendron (Hybrid Pussy Willow)
Salix x reichardtii Hybrid (Pussy Willow)
Salix x rubens (Basket Willow)
Salix viminalis (Basket Willow)
Synonyms - Salix caprea L. = Salix cinerea L.
Salix matsudana Koidzumi = Salix babylonica L.

Family: - Salicaceae

Names:

Salix is Latin for Willow.
Cinerea is Latin for ash coloured referring to the soft grey hairs on the underside of the leaves and greyish bark.
Fragilis is Latin for fragile and refers to the easily broken shoots.
Willow, Sallow
There are 32 different groups of Willows in Australia.
Salix fragilis var. fragilis is called Crack Willow because the brittle wood makes an cracking sound when it breaks.

Other Names:

Osier
Sallow

Summary:

Description:

Deciduous trees or shrubs from 5 to 30 m tall with single or multiple trunks usually along waterways or in wetland. Individual plants are usually male or female and have long, yellow catkin flowers. The group is usually divided into the shrub and tree forms.
White Willow Salix alba is a deciduous tree to 12 m tall with finely toothed leaves and somewhat drooping branchlets.
Weeping Willow Salix babylonica is a deciduous tree to 20 m tall with a stout trunk and has characteristic drooping or weeping, green to brown-green stems with narrow, bright yellow-green leaves and flowers in catkins in spring. It is rarely invasive but may hybridise with invasive Salix species.
Common Sallow (Salix cinerea) is a rounded, multi-stemmed shrub to small tree often 1-2 metres tall and up to 10 metres tall with separate female and male catkins and smooth, grey-brown bark. The leaves are shiny green on top and covered with soft grey hairs underneath. Its flowers appear before the leaves in spring.
Crack Willow (Salix fragilis) is a small, branching tree, that is usually a male clone, up to 25 metres tall with dark-brown to grey deeply fissured bark and spreading rather than drooping branches. The branches make a cracking sound when broken. The leaves are shining on the upper surface and hairless underneath.
Black Willow (Salix nigra) is an erect tree with separate male and female individuals, up to 20 metres tall and dark to black-brown deeply fissured bark.
Basket Willow (Salix x rubens) is a spreading tree with separate female and male individuals, 15-20 metres tall and somewhat wider
Common Osier (Salix viminalis) is a shrub or small tree with crowded leaves and straight branchlets.

Cotyledons:

Two.

First leaves:

Leaves:

Deciduous in winter.
Stipules -
Petiole - less than 20 mm and less than one quarter as long as the lamina.
Blade - Long and narrow (except Pussy Willows) with finely toothed edges and usually paler on the underside.
White Willow (Salix alba)
Stipules -
Petiole - less than 20 mm and less than one quarter as long as the lamina.
Blade - Narrow, elliptic, 30-90 mm long by 6-18 mm wide. Edges finely toothed. Sparsely hairy on the upper side when young. Paler green on the underside and silky hairy and sometimes becoming hairless. Veins more prominent on the topside.
Weeping Willow (Salix babylonica)
Stipules - 5 mm long.
Petiole - 3-10 mm long.
Blade - 50-130 mm long by 5-25 mm wide. Shiny green on top and dull underneath. Edges often irregularly toothed
Common Sallow (Salix cinerea)
Stipules - tiny or to 5 mm long.
Petiole - 2-5 mm long.
Blade - Rounded to broadly lance shaped, 20-90 mm long by 15-40 mm wide with smooth or sometimes toothed edges. Shiny green on the upper surface sometimes with sparse hairs and covered with soft grey hairs on the underside. It rarely looses its hairiness with age. The leaves do not taste bitter.
Crack Willow (Salix fragilis)
Stipules - 3-6 mm long, toothed
Blade - Shiny green on top and lighter green underneath. Hairless. Lance shaped, 50-150 mm long by 10-30 mm wide, usually slightly curved with irregularly toothed edges. May be hairy when young but become hairless with age. The leaves often have red galls produced by the Willow Sawfly (Pontania proxima)
Black Willow (Salix nigra)
Blade - Lance shaped with minutely toothed edges and green topside is almost the same colour as the underside.
Common Osier (Salix viminalis)
Petiole - 2-5 mm long.
Blade - 40-90 mm long by 4-8 mm wide. Green and hairless on top, whitish and densely hairy below. Veins more prominent on the underside. Tip tapering to a point. Edges parallel and smooth. Base tapering.
Basket Willow (Salix x rubens)
Blade - Lance shaped with minutely toothed edges. May be hairy when young but become hairless with age.

Stems:

White Willow (Salix alba) Branchlets often drooping. Grey, fissured bark.
Weeping Willow (Salix babylonica) Drooping, smooth and hairless branchlets. Grey bark becoming deeply fissured with age. Up to 20 m tall.
Common Sallow (Salix cinerea) is multi-stemmed, erect to spreading and up to 10 metres tall but often only 1-2 metres tall with somewhat smooth, grey-brown bark. The branchlets are green to green-brown and often remain hairy in the cinerea (Grey Sallow) subspecies or dark red to brown and often become almost hairless in the oleifolia (Rusty Sallow) subspecies. The branchlets are not brittle.
Crack Willow (Salix fragilis) - Singled to multi-stemmed, up to 25 metres tall with erect and spreading branches and dark-brown to grey deeply fissured, rough bark. Branches often take root where they touch the ground. The branchlets dark-green to brown, upright, brittle and make a cracking sound when broken. Twigs diverge nearly at right angles
Basket Willow (Salix x rubens) 20-25 metres tall with spreading branches and green to orange or dark red, shiny branchlets.
Black Willow (Salix nigra) erect up to 20 metres tall with dark brown to black-brown deeply fissured bark. The branchlets are shiny, hairless and purple-brown.
Common Osier (Salix viminalis) Long, straight, flexible twigs that are grey and hairy when young.

Flower head:

Upright catkins carry many tiny flowers.
Male and female flowers occur on separate catkins or plants.
(Salix alba) Female ale catkins appear with the leaves and are 30-60 mm long.
(Salix babylonica) Female catkins, 10-20 mm long appear with the leaves. Catkins elongate slightly when in fruit. Male plants not recorded in Australia.
Common Sallow (Salix cinerea) has separate male and female catkins that are cylindrical and are stalkless. Catkins appear before the leaves. Male catkins 15-35 mm long by 20 mm wide. Female catkins 20-40 mm long
Crack Willow (Salix fragilis) only produces male, cylindrical catkins, 40-75 mm long that spread or curve downwards. Catkins appear with the leaves.
Common Osier (Salix viminalis) Male catkins cylindrical, 20-30 mm long, stalkless and appear before the leaves.

Flowers:

Shrub Willows have black flower scales whereas tree Willows have pale scales.
Often fragrant
Ovary - Superior.
Perianth -
Stamens - 1-15
Anthers -
Common Sallow (Salix cinerea) has short densely hairy bracts.
Crack Willow (Salix fragilis) has elliptic to linear bracts.
Common Osier (Salix viminalis) has hairy bracts that are darker brown at the apex.

Fruit:

A two valved capsule containing many tiny seeds.
White Willow (Salix alba) stalkless.
(Salix babylonica) Does not produce fruit in Australia because no male plants are here.
Common Sallow (Salix cinerea) Cylindrical, silky hairy.
Crack Willow (Salix fragilis) does not produce fruit as female plants are rare. (Capsule conical and shortly stalked overseas.)

Seeds:

Small with long silky hairs (pappus) attached to one end.

Roots:

Large, dense, woody, branching root mats are formed on the soil surface or in shallow, slow moving water.
Crack Willow (Salix fragilis) forms bright red rootlets when in or near water.

Key Characters:

Deciduous, dioecious tree.
Leaves alternate and with a petiole that is less than 20 mm and less than one quarter as long as the lamina.
Winter buds with a single outer scale.
Inflorescence a dense spike like catkin with greatly reduced flowers subtended by a scale-like bract.
Seeds small with a tuft of silky hairs.
Never forms suckers from roots.
Adapted from Gwen Harden

Biology:

Life cycle:

Seed germinates from October to February.
Mature trees or shrubs flower from September to October and set seed from October to November. Seeds ripen about 3-4 weeks after flowering and are usually dropped before the end of December. Seeds have generally lost viability by the end of February. Seedlings emerge as soon as the seed encounters wet bare soil conditions and grow rapidly. Most plants can breed 2-8 years after germination.
Twigs and stem fragments broken from the parent may float downstream and take root where they lodge.
The flowers appear with the new leaves in Spring with Crack Willow (Salix fragilis), Basket Willow (Salix x rubens) and Black Willow (Salix nigra).
In Common Sallow (Salix cinerea) the flowers appear before the leaves in spring.

Physiology:

Some species will tolerate frosts to -40 degrees C.
Most tolerate waterlogging.

Reproduction:

Most are dioecious have separate male and female plants. In Australia most species are single sex clones but will readily hybridise and produce seed when they are growing close to species of the opposite sex that flower at the same time.
At least 12 taxa in Australia produce seed.
Crack Willow (Salix fragilis) mainly reproduces vegetatively and will hybridise with at least three other species.
Basket Willow (Salix x rubens) reproduces from seed and vegetatively.
Black Willow (Salix nigra), Common Sallow (Salix cinerea), White Willow (Salix alba) reproduces from seed and vegetatively and hybridises with other Salix species
New Zealand or Tortured Willow (Salix matsudana) reproduces vegetatively and will hybridise with other Salix species.

Flowering times:

September to October and sets seed from October to November in Victoria and NSW. Flowers usually only last 2-3 weeks.
Flowers recorded from August to November in Victoria.
Common Sallow (Salix cinerea) September to October in NZ.
Crack Willow (Salix fragilis) September to October in NZ.

Seed Biology and Germination:

The seeds usually only remain viable for a few days to six weeks.
Seeds germinate within 24 hours of exposure to favourable conditions.

Vegetative Propagules:

Stems and twigs readily take root. Regrows (coppices) readily from stumps.

Hybrids:

Many hybrids are formed between the various species. This process may result in apparently benign species becoming invasive.

Allelopathy:

Population Dynamics and Dispersal:

Stem fragments are a major source of spread for many species. Some species produce seed which is carried by wind or water usually less than a kilometre but potentially up to 100 km.
Seed is the main method of spread for some species like the Grey Sallow and Black Willow.
It has no soil seed bank or dormant seed.
Germination and recruitment from seed is usually restricted to areas that are at least continuously wet for several months after seed fall in summer.
Often spread in garden refuse.
Also spread by intentional planting, landfill and earthmoving equipment.
Many species are still available in nurseries.
About 5% of the potential range of Willows is currently infested.
Species that spread by stem fragments tend to have very brittle twigs that break in high winds or floods. Those spreading by seed tend to have pliable wood.

Origin and History:

Northern hemisphere generally.
Salix alba var. vitellina (White Willow) Eurasia and North Africa
Salix babylonica L. (Weeping Willow) Northern China, Eastern Asia, South Africa, New Zealand, North America, South America
Salix cinerea L. (Common Sallow or Grey Sallow) Europe, Western Asia, North Africa, New Zealand
Salix fragilis var. fragilis (Crack Willow) Eurasia
Salix nigra Marshall (Black Willow) USA
Salix x calodendron (Hybrid Pussy Willow)
Salix x reichardtii Hybrid (Pussy Willow)
Salix x rubens (Basket Willow) Europe
Salix viminalis (Basket Willow) Eurasia

Distribution:

ACT, NSW, SA, TAS, VIC, WA.
WA only has Salix babylonica or Weeping Willow naturalised and is beginning to spread from plantings on the Swan Coastal Plain.
The largest naturalised infestations are in Victoria, Tasmania, New South Wales and the Australian Capital Territory.
Salix alba var. vitellina (White Willow) ACT, NSW,TAS, VIC
Salix babylonica L. (Weeping Willow) ACT, NSW, TAS, VIC, WA
Salix cinerea L. (Common Sallow or Grey Sallow) ACT, NSW, SA, TAS, VIC
Salix fragilis var. fragilis (Crack Willow) ACT, NSW, SA, TAS, VIC
Salix matsudana hybrids (New Zealand Willow or Tortured Willow) NSW, VIC
Salix nigra Marshall (Black Willow) ACT, NSW, VIC. It is most troublesome in southern NSW, north eastern VIC and the Australian Alps region.
Salix viminalis (Basket Willow) NSW
Salix x calodendron (Hybrid Pussy Willow)
Salix x reichardtii Hybrid (Pussy Willow)
Salix x rubens (Basket Willow) ACT, NSW,SA, TAS, VIC.

Yellow = Salix alba. Blue = Salix babylonica. Red = Salix cinerea. White = Salix fragilis.
Courtesy Australia's Virtual Herbarium.

Habitats:

Sea level to alpine wetlands.
Freshwater riparian areas.
Common Sallow (Salix cinerea) prefers cool, moist places from the coast (especially behind dunes) to mountains and is common in swamps and can become the dominant vegetation in swamps.
Crack Willow (Salix fragilis) prefers temperate, wet areas, waterways and lakesides.

Climate:

Temperate

Soil:

Permanently or seasonally wet or water logged soils.

Plant Associations:

Paperbarks and wetland species. Some species tend to form a monoculture after invasion.

Significance:

Weed of National Significance (WONS). Weeping Willow (Salix babylonica) and two Hybrid Pussy Willows (Salix x calodendron and Salix x reichardtii) are not Weeds of National Significance but can hybridise with other Willows which don't produce seeds.
Estimated to occupy thousands of kilometres of stream banks.
The introduction of New Zealand Willow is likely to cause significant problems because it produces large amounts of seed and the males will fertilise the Weeping Willow (Salix babylonica) which until now has been largely barren.

Beneficial:

Previously planted along water ways for erosion control.
Used for windbreaks, shade, fodder, basket weaving, timber and cricket bats.
Ornamental.
Source of pollen for bees.
Weeping Willow (Salix babylonica) has not has not spread widely and could be monitored for signs of seed set by hybridising with other species or evidence of increased spread rather than actively controlled in many situations.

Detrimental:

Invasive along water courses and in wetlands. Roots spread into stream beds reducing water flows, diverting water from the main channel and creating upstream flooding. Leaf drop in autumn can cause organic matter contamination and reduction in oxygen levels in water.
May reduce habitat for native and aquatic species.
Displaces native vegetation often forming monocultures.
Debris and sediment caught by the Willows may divert water which may lead to erosion.
Dense shade over summer can reduce light levels and water temperatures which affect aquatic life.
Grey Sallow (Salix cinerea) is the most invasive of the Willows.
Salix babylonica has replaced much of the indigenous River Oak (Casuarina cunninghamiana) on the creek banks in the ACT.
About $2m/year spent on Willow control in Victoria.

Toxicity:

May cause bloat especially if animals drink soon after eating leaves.

Symptoms:

Bloat.

Treatment:

Remove stock from infested area. Deny stock access to water for several hours. Treat as for bloat if necessary.

Legislation:

Sale and trade of some species is banned in some states.
Legislation in NSW and ACT.

Management and Control:

Don't plant ornamental Willow species near naturalised Willows, wetlands or streams.
Start control programs from the top of the catchment to reduce reinfestation by stem fragments. Identify and map seed producing trees of Pussy and Black Willow up to 2 km from the stream or wetland areas and remove these first.
Consider the risks or increased erosion and downstream flooding after Willow removal. Plant or encourage alternate species before removal of Willows. Clear downstream areas that may create flooding.
Carefully plan control program as wholesale removal of infestations may cause significant erosion and flooding problems.
Plants on banks that have been killed with herbicides may need to be cleared once dead to prevent them falling over and destabilising banks or falling into the stream and impeding water flows.
Leave root systems in the soil to help stabilise the area.
Mechanical control with bulldozers is generally only partially effective in wet areas because of the stem that are fragments broken and pushed into the soil readily establish new plants. It is more effective on dry sites.

Thresholds:

Eradication strategies:

In areas where trees can be left, spray or paint the lower 50 cm of each trunk with 1 L of Access® in 15 L diesel with best results in the summer and autumn. Stem injection may be more effective on the species with deeply fissured bark but is considerably slower. Inject the trees as close to the crown as possible with an injection site every 10 cm around the trunk or base and apply 2 mL of neat glyphosate per cut or site. Injection sites may be made with a tomahawk or chisel to penetrate the sapwood or a 1 cm drill 2-4 cm deep angled down at 45 degrees. Stem injections appear to work best in autumn just before the leaves change colour.
Trees with trunks less than 10 cm diameter can be cut in autumn and the stump immediately painted with neat glyphosate or 1 part Access® in 15 parts diesel. Tops should be moved to dry ground to prevent them taking root. Cutting alone is ineffective because the tree readily re-sprouts.
Foliar spraying with 1 L glyphosate in 100 L water can be used on smaller trees, shrubs, seedling infestations or regrowth from other treatments during summer to autumn when leaves are present.
In areas where trees need to be physically removed, consider killing them with herbicides some months before removal or cut the trunk between ground level and the first branches and immediately paint the cut stump with neat glyphosate or 1 part Access® in 15 parts diesel. Remove and burn all the trees and debris to prevent stem fragments reinfesting the site. New plants can establish from chips so if trees are to be chipped they should be chemically killed first or chipped on a dry site and inspected 1-2 years later and sprayed if necessary with 1 part glyphosate in 100 L water.
Revisit the site every 2 years to remove new plants before they set seed or get too big for hand removal.
Plants less than 50 cm tall are fairly easy to pull and most species rarely sucker from small broken roots. If it breaks off at ground level then the root usually needs to be removed. The pulled material needs to be taken to a dry site to prevent it re-establishing.

Herbicide resistance:

None reported and in vegetatively reproducing species none is expected to occur.

Biological Control:

Related plants:

It is very difficult to identify the different species of naturalised Willows.
Basket Willow (Salix x rubens) Single or multi-stemmed trees. Often planted for stream bank stabilisation.
Black Willow (Salix nigra). Tree.
Crack Willow (Salix fragilis var. fragilis) Single or multi-stemmed trees. Often planted for stream bank stabilisation. Spreads almost entirely by stem fragments and is consequently almost entirely along water flow lines.
New Zealand Willow (Salix matsudana hybrids)
Pussy Willow hybrids Salix x calodendron and Salix x reichardtii)
Grey Sallow or Pussy Willow (Salix cinerea) A large spreading shrub to small tree with branches that are hard to snap. Produces seed and many seedlings.
Weeping Willow (Salix babylonica)

Plants of similar appearance:

References:

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P6.

Blood, K. (2001). Environmental weeds: a field guide for SE Australia. (CH Jerram & Associates, Australia). P34-35. Photos.

Cremer KW (1995) 'Willow identification for river management in Australia.' (NSW Agriculture and CSIRO)

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume 1. P450-451. Diagrams.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P212.

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). P158, #876.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P140.

Muyt, A. (2001). Bush Invaders of South-East Australia: a guide to the identification and control of environmental weeds found in South East Australia. (R.G and F.J. Richardson, Australia). P249-252. Photos.

Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn). P. Photo.

Roy, B., Popay, I., Champion, P., James, T. and Rahman, A. (1998). An Illustrated Guide to Common Weeds of New Zealand. (New Zealand Plant Protection Society). P273-274. Photo

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.