Willow

Willows (Salix) are a genus of around 400 species^[1] of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere. Some of the shrub and smaller tree species may also be known by the common names osier and sallow; the latter name is derived from the same root as the Latin salix. Some willows, particularly arctic and alpine species, are very small; the Dwarf Willow (Salix herbacea) rarely exceeds 6 cm in height, though spreading widely across the ground.

Willows are very cross-fertile and numerous hybrids occur, both naturally occurring and in cultivation. A well known example is the Weeping Willow (Salix × sepulcralis), very widely planted as an ornamental tree, which is derived from hybridisation between the Chinese Peking Willow and the European White Willow.

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Description

The willows all have abundant watery juice, furrowed scaly bark which is heavily charged with salicylic acid, soft, pliant, tough wood, slender branches and large fibrous often stoloniferous roots. These roots are remarkable for their toughness, size, and tenacity of life.

The leaves are typically elongated but may also be round to oval, frequently with a serrated margin. All the buds are lateral; no absolutely terminal bud is ever formed. These are covered by a single scale, inclosing at its base two minute opposite buds, alternate with two, small, scale-like, fugacious, opposite leaves. The leaves are alternate except the first pair which fall when about an inch long. They are simple, feather-veined, and typically linear-lanceolate. Usually they are serrate, rounded at base, acute or acuminate. In color they show a great variety of greens, ranging from yellow to blue.

Flowers

Willows are dioecious with male and female flowers appearing as catkins on different plants; the catkins are produced early in the spring, often before the leaves or as the new leaves open. The petioles are short, the stipules often very conspicuous, looking like tiny round leaves and sometimes remaining for half the summer. On some species, however, they are small, inconspicuous, and fugacious.

The staminate flowers are without either calyx or corolla; they consist simply of stamens, in number varying from two to ten, accompanied by a nectariferous gland and inserted on the base of a scale which is itself borne on the rachis of a drooping raceme called a catkin, or ament. This scale is oval and entire and very hairy. The anthers are rose colored in the bud but orange or purple after the flower opens, they are two-celled and the cells open longitudinally. The filaments are threadlike, usually pale yellow, often hairy.

The pistillate flowers are also without calyx or corolla; and consist of a single ovary accompanied by a small flat gland and inserted on the base of a scale which is likewise borne on the rachis of a catkin. The ovary is one-celled, the style two-lobed, and the ovules numerous.

Fruit

The fruit is a small capsule containing numerous tiny (0.1 mm) seeds embedded in white down, which assists wind dispersal of the seeds. The fruit is a one-celled, two-valved, cylindrical, beaked capsule, containing many minute seeds which are furnished with long, silky, white hairs. The catkins appear before or with the leaves.

Cultivation

Almost all willows take root very readily from cuttings or where broken branches lie on the ground. There are a few exceptions, including the Goat Willow and Peachleaf Willow. One famous example of such growth from cuttings involves the poet Alexander Pope, who begged a twig from a parcel tied with twigs sent from Spain to Lady Suffolk. This twig was planted and thrived, and legend has it that all of England's Weeping Willows are descended from this first one.^[2]

Willows are often planted on the borders of streams in order that their interlacing roots may protect the bank against the action of the water. Frequently the roots are much larger than the stem which grows from them.

Ecological issues

Willows are used as food plants by the larvae of some Lepidoptera species - see list of Lepidoptera that feed on willows.

A number of willow species were widely planted in Australia, notably as erosion control measures along watercourses. They are now regarded as an invasive weed and many catchment management authorities are removing them to be replaced with native trees.^[3][4]

Uses

Medicinal uses

The leaves and bark of the willow tree have been mentioned in ancient texts from Assyria, Sumer and Egypt^[5] as a remedy for aches and fever,^[6] and the Greek physician Hippocrates wrote about its medicinal properties in the 5th century BC. Native Americans across the American continent relied on it as a staple of their medical treatments. This is because they contain acetylsalicylic acid, also known as aspirin.

In 1763 its medicinal properties were observed by the Reverend Edward Stone in England. He notified the Royal Society who published his findings. The active extract of the bark, called salicin, 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 is acidic when in a saturated solution in water (pH = 2.4), and is called salicylic acid for that reason.

In 1897 Felix Hoffmann created a synthetically altered version of salicin (in his case derived from the Spiraea plant), which caused less digestive upset than pure salicylic acid. The new drug, formally Acetylsalicylic acid, was named aspirin by Hoffmann's employer Bayer AG. This gave rise to the hugely important class of drugs known as non-steroidal anti-inflammatory drugs (NSAIDs).

Other uses

Uses as a plant 

Agroforestry, Biofiltration, Constructed wetlands, Ecological wastewater treatment systems, Hedges, Land reclamation, Landscaping, Phytoremediation, Streambank stabilisation (bioengineering), Slope stabilisation, Soil erosion control, Shelterbelt & windbreak, Soil building, Soil reclamation, Tree bog compost toilet, Wildlife habitat

Agriculture 

Willow bark contains auxins, plant growth hormones, especially those used for rooting new cuttings. The bark can even be used to make a simple extract that will promote cutting growth.

Uses as energy source 

Charcoal, Energy forestry such as the Willow Biomass Project

Uses of wood 

Basket weaving, Box, Brooms, Cricket bats, Cradle boards, Chairs & furniture, Dolls, Fish traps, Flutes, Poles, Sweat lodges, toys, turnery, tool handles, Veneer, Wands, Wattle fences, Wattle and daub, whistles

Uses of wood-derived products

Fibre plants, Paper, Rope and string, Tannin

• As part of the four species used on the Jewish holiday of Sukkot.
• Living Willow Sculpture

Willow in human culture

The willow is a famous subject in many East Asian nations' cultures, and the image has been employed in a variety of Korean poetry. Gisaeng Hongrang, who lived in the middle of the Joseon period, wrote: like willow I will be the willow on your bedside. Hongrang wrote this poem by the willow in the rain in the evening which gave to her parting lover. ^[7]

Pictures

See also

• Willow-herb is the common name of several species of Epilobium
• Seep willow is the common name of Baccharis salicifolia
• Aravah, the Hebrew name of the willow, for its ritual use during the Jewish Feast of Tabernacles
• Pyongyang, city of willow, North Korea's capital

References

• Keeler, Harriet L. (1900). Our Native Trees and How to Identify Them. New York: Charles Scriber's Sons, 393-395. 
• Newsholme, C. (1992). Willows: The Genus Salix. ISBN 0-88192-565-9
• Warren-Wren, S.C. (1992). The Complete Book of Willows. ISBN 0-498-01262-X