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Genus Salix Family Salicaceae

Description: Trees or shrubs, winter buds with a single, non-sticky outer scale.

Leaves mostly deciduous, mostly linear to elliptic to oblong, margins mostly toothed; petiole less than a quarter as long as lamina.

Floral bracts entire or finely toothed; flowers with 1 or 2 tongue-like glands or rarely a small cup-like gland. Stamens 1–15, filaments free or fused. Ovary mostly 2-carpellate, ovules 4–many, stigma entire or 2-lobed, sessile or on a slender style.

Capsule 2-valved; seeds with silky hairs.


Distribution and occurrence: World: c. 400 spp., mainly temperate & subarctic regions of N. Hemisphere, a few species extending into the tropical & S. Hemisphere. Australia: 12–14 species and several hybrids (some named) naturalised, and many more cultivated.

Most species were introduced into Australia as potential economic plants, for timber, basketry or soil stabilisation, or as ornamentals. As willow seed is very short-lived, all of the early introductions of willows were made as cuttings or pot plants. This meant that most of the plants of any species, or at least the plantings at any one site, were derived from one or very few individuals. As plants are mostly either male or female this has meant that most of the clones were unisexual and plantings rarely produced seed or seedlings. Seed was only possible from hybridisation of two different species where the correct sexes were present, the flowering times overlapped, and the trees were less than 500 m apart (about the maximum effective distance for the pollinating insects). The sparsity of overlap of flowering times for the different species has meant that seeds were rarely formed. Over the years more species and cultivars have been introduced. Some of these cultivars were hybrids between other species, often very rare hybrids. If such hybrids are planted, and either or both parent species are around, they can overcome the problems of non-overlapping flowering times, and also reduce the inter-species fertility barriers. Simply increasing plantings has allowed a greater opportunity for trees to cross pollinate. With both types of increased plantings there is now an opportunity for fertile and viable seed to be formed. Also, as the trees aged, the longer they tended to flower and the more likely that overlaps occurred. Air travel has also meant viable seed could be imported, producing mixed-sex populations of some species. All such situations have occurred and there are now areas where there has been mass colonisation by seedling wilows.

Identification: For positive identification of species, hybrids and cultivars, it may be necessary to collect from the same tree when flowering in spring and in full leaf in summer. The leaves should be collected from branch systems that have borne flowers the current season and not from the vigorous sterile shoots arsing from near the base.

The ridges in key lead 17, are the ridges that are present on the wood underneath the bark (strip bark to see).

Key based on Meikle, R.D. (1984); Carr G.W. (1996); and Cremer, K.W. (1995) and parts of the original treatment in Flora of N.S.W. (1990).

Text by S.W.L. Jacobs & L. Murray (2000)
Taxon concept: Flora of NSW 1 Suppl. (2000)

 Key to the species 
1Trees narrow-columnar mostly evergreen (usually 30% of leaves retained over winter); male clone, usually only a few catkins produced with little pollenSalix humboldtiana
Trees or shrubs, not columnar; always completely deciduous; male and/or female clones; male catkins usually producing ample fertile pollen2
2Trees; with single or several trunks, 10–20 m high; leaves emerging with catkins; flower scales pale green or yellow; leaves mainly lanceolate3
Multi-stemmed shrubs or trees with 5–50 or more stems, to 4–9 m high; leaves emerge long after catkins (except Salix purpurea); flower scales dark; leaf shape variable
                       Back to 1
13
3Branches and leaves contortedSalix matsudana
Branches and leaves not contorted
                       Back to 2
4
4Penultimate branches weeping (ultimate branches are short lateral branches on weeping branches)5
No branches particularly weeping, although some may droop
                       Back to 3
8
5Bark of twigs and branches very golden, both sexes present, sometimes on the same catkinSalix x sepulcralis
Bark of twigs and branches not markedly golden; male or female
                       Back to 4
6
6Catkins 15–20 mm long; catkin stalks 2–3 mm long; ovary pear shaped; mostly femaleSalix babylonica
Catkins >20 mm long; catkin stalks >3 mm long; ovary more slender, flask-shaped, gradually tapering towards the top; male or female
                       Back to 5
7
7Leaves ± hairy; ovary not much larger than the flower scale; Salix x Salix alba; both sexes presentSalix x sepulcralis
Leaves ± hairless; ovary far longer than flower scale; Salix babylonica x Salix fragilis; male or female
                       Back to 6
Salix x pendulina
8Branches yellow to orange for more than 1 m from tips; may weep in lower crownSalix alba
Branches not yellow, not weeping
                       Back to 4
9
9Young twigs and branchlets exposed to full light usually a dark reddish brown; catkins of both sexes with flowers not crowded on the rhachisSalix nigra
Young twigs and branchlets greenish even when exposed to full light; usually only catkins of one sex present in a population (unless established from seed), or rarely bisexual catkins, and the flowers crowded on the rhachis of the catkin
                       Back to 8
10
10Shoots and leaves sparsely pubescent at first, becoming glabrescent11
Hairs on shoots, twigs and leaves ± persistent
                       Back to 9
Salix alba
11Twigs break easily with a audible crack; fairly stout and rigidSalix x fragilis
Twigs flexible (do not break readily); slender
                       Back to 10
12
12Single prominent stem with a narrow crown when young; catkins usually <5 mm wide and <5 cm long; often cultivated as orchard windbreaks but hybridizes with other species to form seedling armsSalix matsudana x alba
One or more prominent stems with a ± rounded crown; catkins often >5 mm wide and/or >5 cm long; usually growing as seedling swarms from crossing between Salix alba and Salix x fragilis, rarely cultivated
                       Back to 11
Salix x rubens
13Leaves glabrous14
Leaves with hairs
                       Back to 2
15
14Leaves and catkins ± oppositeSalix purpurea
Leaves and catkins alternate
                       Back to 13
Salix glaucophylloides
15Leaves with recurved margins and no apparent toothing16
Leaves not recurved and with margins ± toothed
                       Back to 13
17
16Leaves linear or linear-lanceolate, the margins almost parallel to one anotherSalix viminalis
Leaves lanceolate to ovate-lanceolate, the margins distinctly convex, not parallel
                       Back to 15
Salix x sericans
17Ridges on 1 cm diam. branches strong (typically 1x1x10–40 mm); crown tends to spread from an early age; lower surface of leaf may have some rust coloured hairsSalix cinerea
Ridges weak (0.5x0.5x5–10 mm); crown erect, except when old; no rust-coloured hairs
                       Back to 15
18
18Male only; catkins ovoid, 20–35 mm long, spreading; eaves 50–100 mm long, ovoid; widely planted for ornamentSalix x reichardtii
Female only (sterile); catkins cylindrical, 30–60 mm long, narrow-ovoid; planted for erosion control
                       Back to 17
Salix x calodendron

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