White willow

Salix alba
Willow family (Salicaceae)


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Salix alba, the white willow, is a species of willow native to Europe and western and central Asia. The name derives from the white tone to the undersides of the leaves.

It is a medium-sized to large deciduous tree growing up to 10–30 m tall, with a trunk up to 1 m diameter and an irregular, often-leaning crown. The bark is grey-brown, and deeply fissured in older trees. The shoots in the typical species are grey-brown to green-brown. The leaves are paler than most other willows, due to a covering of very fine, silky white hairs, in particular on the underside; they are 5–10 cm long and 0.5–1.5 cm wide. The flowers are produced in catkins in early spring, and pollinated by insects. It is dioecious, with male and female catkins on separate trees; the male catkins are 4–5 cm long, the female catkins 3–4 cm long at pollination, lengthening as the fruit matures. When mature in midsummer, the female catkins comprise numerous small (4 mm) capsules, each containing numerous minute seeds embedded in white down, which aids wind dispersal.

Ecology

Like all willows, Salix alba is usually to be found in wet or poorly-drained soil at the edge of pools, lakes or rivers. Its wide-spreading roots take up moisture from a large surrounding area.

White willows are fast-growing, but relatively short-lived, being susceptible to several diseases, including watermark disease caused by the bacterium Brenneria salicis (named because of the characteristic 'watermark' staining in the wood; syn. Erwinia salicis) and willow anthracnose, caused by the fungus Marssonina salicicola. These diseases can be a serious problem on trees grown for timber or ornament.

It readily forms natural hybrids with crack willow Salix fragilis, the hybrid being named Salix × rubens Schrank.

Varieties, cultivars and hybrids

A number of cultivars and hybrids have been selected for forestry and horticultural use:

  • Salix alba 'Caerulea' (cricket-bat willow; syn. Salix alba var. caerulea (Sm.) Sm.; Salix caerulea Sm.) is grown as a specialist timber crop in Britain, mainly for the production of cricket bats, and for other uses where a tough, lightweight wood that does not splinter easily is required. It is distinguished mainly by its growth form, very fast-growing with a single straight stem, and also by its slightly larger leaves (10–11 cm long, 1.5–2 cm wide) with a more blue-green colour. Its origin is unknown; it may be a hybrid between white willow and crack willow, but this is not confirmed.
  • Salix alba 'Vitellina' (golden willow; syn. Salix alba var. vitellina (L.) Stokes) is a cultivar grown in gardens for its shoots, which are golden-yellow for one to two years before turning brown. It is particularly decorative in winter; the best effect is achieved by coppicing it every two to three years to stimulate the production of longer young shoots with better colour. Other similar cultivars include 'Britzensis', 'Cardinal', and 'Chermesina', selected for even brighter orange-red shoots.
  • Salix alba 'Vitellina-Tristis' (golden weeping willow, synonym 'Tristis') is a weeping cultivar with yellow branches that become reddish-orange in winter. It is now rare in cultivation and has been largely replaced by Salix x sepulcralis 'Chrysocoma'. It is, however, still the best choice in very cold parts of the world, such as Canada, the northern US, and Russia.
  • The golden hybrid weeping willow (Salix × sepulcralis 'Chrysocoma') is a hybrid between white willow and Peking willow Salix babylonica.

Award of Garden Merit

The following have received the Royal Horticultural Society's Award of Garden Merit

  • Salix alba 'Golden Ness'
  • Salix alba var. serica (silver willow)
  • Salix alba var. vitellina 'Yelverton'
  • Salix × sepulcralis 'Erythroflexuosa'
  • Salix × sepulcralis var. chrysocoma

Uses

The wood is tough, strong, and light in weight, but has minimal resistance to decay. The stems (withies) from coppiced and pollarded plants are used for basket-making. Charcoal made from the wood was important for gunpowder manufacture. The bark tannin was used in the past for tanning leather. The wood is used to make cricket bats. S. alba wood has a low density and a lower transverse compressive strength. This allows the wood to bend, which is why it can be used to make baskets. Willow bark contains indole-3-butyric acid, which is a plant hormone stimulating root growth; willow trimmings are sometimes used to clone rootstock in place of commercially synthesized root stimulator. It is also used for ritual purposes by Jews on the holiday of Sukkot.

Medicinal uses

Willow (of unspecified species) has long been used by herbalists for various ailments, although it is a myth that they attribute to it any analgesic effect. One of the first references to White Willow specifically was by Edward Stone, of Chipping Norton, Oxfordshire, England, in 1763. He 'accidentally' tasted the bark and found it had a bitter taste, which reminded him of Peruvian Bark (Cinchona), which was used to treat malaria. After researching all the 'dispensaries and books on botany,' he found no suggestion of willow ever being used to treat fevers, and decided to experiment with it himself. Over the next seven years he successfully used the dried powder of willow bark to cure 'agues and intermittent fevers' of around fifty people, although it worked better when combined with quinine.

Stone appears to have been largely ignored by the medical profession and herbalists alike. There are reports of two pharmacists trialling this remedy, but no evidence that it worked. By the early 20th century, Maud Grieve, one of the most famous herbalists of the era, did not consider White Willow to be a febrifuge. Instead, she describes using the bark and the powdered root for its tonic, antiperiodic and astringent qualities and recommended its use in treating dyspepsia, worms, chronic diarrhoea and dysentery. She considered tannin to be the active constituent.

An active extract of the bark, called salicin, after the Latin name Salix, was isolated to its crystalline form in 1828 by Henri Leroux, a French pharmacist, and Raffaele Piria, an Italian chemist, who then succeeded in separating out the acid in its pure state. Salicylic acid is a chemical derivative of salicin, and is widely used in medicine. Acetylsalicylic acid (Aspirin) is, however, a chemical that does not occur in nature and which was originally synthesised from salicylic acid extracted from Meadowsweet, and is not connected to willow except in the similarity of its name.

References

Further reading

  • Morader, H. L.; Prego, I. A.; Facciuto, G. R.; Maldonado, S. B. (November 2000). "Storage Behavior of Salix alba and Salix matsudana Seeds". Annals of Botany. 86 (5): 1017–1021. doi:10.1006/anbo.2000.1265. JSTOR 42770865.
  • van Casteren, A.; Sellers, W. I.; Thorpe, S. K. S. (23 November 2011). "Why don't branches snap? The mechanics of bending failure in three temperate angiosperm trees". Trees. 26 (3): 789–797. doi:10.1007/s00468-011-0650-y. S2CID 17867624.
  • Vennetier, Michel (February 2015). "Tree root architecture: new insights from a comprehensive study on dikes" (PDF). Plant and Soil. 387 (1–2): 81–101. doi:10.1007/s11104-014-2272-9. S2CID 15729821.

External links

  • Media related to Salix alba at Wikimedia Commons
  • Salix alba — information, genetic conservation units and related resources. European Forest Genetic Resources Programme (EUFORGEN)
  • Salix alba in the CalPhotos photo database, University of California, Berkeley
  • "Salix alba". Calflora. Berkeley, California: The Calflora Database.
  • "Salix alba". Plants for a Future.
  • "Salix alba caerulea". Plants for a Future.
  • "Salix alba vitellina". Plants for a Future.

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