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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, 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, particularly 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, lenghtening as the fruit matures. When mature in mid summer, the female catkins comprise numerous small (4 mm) capsules each containing numerous minute seeds embedded in white down which aids wind dispersal.
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.
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 was used in the past for tanning leather.
Cultivars and hybrids
Hippocrates wrote in the 5th century BC about a bitter powder extracted from willow bark that could ease aches and pains and reduce fevers. This remedy is also mentioned in texts from ancient Egypt, Sumer, and Assyria. The Reverend Edmund Stone, a vicar from Chipping Norton in Oxfordshire England, noted in 1763 that willow bark was effective in reducing a fever.
The 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. Salicin, like aspirin, is a chemical derivative of salicylic acid.
Photographs and illustration
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Salix_alba". A list of authors is available in Wikipedia.|