Willow

Willow
Salix alba 'Vitellina-Tristis' Morton Arboretum acc. 58-95*1
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Malpighiales
Family:	Salicaceae
Tribe:	Saliceae[1]
Genus:	Salix L.
Species
About 400.[2] See List of Salix species

Willows, sallows, and osiers form the genus Salix, around 400 species^[2] of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere. Most species are known as willow, but some narrow-leaved shrub species are called osier, and some broader-leaved species are referred to as sallow (from Old English sealh, related to the Latin word salix, willow). Some willows (particularly arctic and alpine species) are low-growing or creeping shrubs; for example the Dwarf Willow (Salix herbacea) rarely exceeds 6 cm (2 in) in height, though spreading widely across the ground.

Willows are very cross-fertile, and numerous hybrids occur, both naturally and in cultivation. A well-known ornamental example is the Weeping Willow (Salix × sepulcralis), which is a hybrid of Peking Willow (Salix babylonica) from China and White Willow (Salix alba) from Europe.

Description

Willows all have abundant watery bark, sap which is heavily charged with salicylic acid, soft, usually pliant, tough wood, slender branches, and large, fibrous, often stoloniferous roots. The roots are remarkable for their toughness, size, and tenacity to life, and roots readily grow from aerial parts of the plant.

The leaves are typically elongated but may also be round to oval, frequently with a serrated margin. Most species are deciduous; semi-evergreen willows with coriaceous leaves are rare, e.g. Salix micans and S. australior in the eastern Mediterranean. All the buds are lateral; no absolutely terminal bud is ever formed. The buds are covered by a single scale, enclosing at its base two minute opposite buds, alternately arranged, with two small, opposite, scale-like leaves. This first pair soon fall, and the later leaves are alternately arranged. The leaves are simple, feather-veined, and typically linear-lanceolate. Usually they are serrate, rounded at base, acute or acuminate. The leaf 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 (soon falling). In color the leaves show a great variety of greens, ranging from yellowish to bluish.

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 staminate (male) flowers are without either calyx or corolla; they consist simply of stamens, varying in number 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, and often hairy.

The pistillate (female) flowers are also without calyx or corolla; and consist of a single ovary accompanied by a small flat nectar 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

Open capsules of Salix cinerea with seeds and hairs

The fruit is a small, one-celled, two-valved, cylindrical beaked capsule containing numerous tiny (0.1 mm) seeds. The seeds are furnished with long, silky, white hairs, which allow the fruit to be widely dispersed by the wind.

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 (Salix caprea) and Peachleaf Willow (Salix amygdaloides). 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.^[3]

Willows are often planted on the borders of streams so 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 small 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.^[4][5]

Willow roots grow widespread and are very aggressive in seeking out moisture; for this reason, they can become problematic when planted in residential areas, where the roots are notorious for clogging French drains, drainage systems, weeping tiles, septic systems, storm drains, and sewer systems, particularly older, tile, concrete, or ceramic pipes. Newer, PVC sewer pipes are much less leaky at the joints, and are therefore less susceptible to problems from willow roots; the same is true of water supply piping.^[6][7]

Uses

Medicine

The leaves and bark of the willow tree have been mentioned in ancient texts from Assyria, Sumer and Egypt^[8] as a remedy for aches and fever,^[9] and the Ancient 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 it contains salicylic acid, the precursor to 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).

Manufacturing

Willow wood is also used in the manufacture of boxes, brooms, cricket bats (grown from certain strains of white willow), cradle boards, chairs and other furniture, dolls, flutes, poles, sweat lodges, toys, turnery, tool handles, veneer, wands and whistles.

In addition tannin, fibre, paper, rope and string, can be produced from the wood. Willows are also popular for wicker (often from osiers), which is used in basket weaving, fish traps, wattle fences and wattle and daub.

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.

Male catkin of Salix cinerea with bee

Willows produce a modest amount of nectar that bees can make honey from, and are especially valued as a source of early pollen for bees.

Energy

Willow is grown for biomass or biofuel, in energy forestry systems, as a consequence of its high energy in-energy out ratio, large carbon mitigation potential and fast growth.^[10] Large scale projects to support willow as an energy crop are already at commercial scale in Sweden^[11] , and in other countries there are being developed through initiatives such as the Willow Biomass Project in the US and the Energy Coppice Project in the UK.^[12]

Willow may also be grown to produce Charcoal.

Environment

As a plant, willow is used for 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.

Art

Woodbine caused by Honeysuckle on a Willow.

Willow is used as charcoal (for drawing) and in living sculptures. Living sculptures are created from live willow rods planted in the ground and woven into shapes such as domes and tunnels. Willow stems are used to weave baskets and 3 dimensional sculptures such as animals and figures. Willow stems are also used to create garden features such as decorative panel and obelisks.

Religion

In religion, willow is one of the "Four Species" used in a ceremony on the Jewish holiday of Sukkot. In Buddhism, a willow branch is one of the chief attributes of Kwan Yin, the bodhisattva of compassion. Willow is also one of the "nine sacred trees" mentioned in Wicca and witchcraft, with several magical uses. In the Wiccan Rede, it is described as growing by water, guiding the dead to "The Summerland", a commonly used term in Wicca to refer to the afterlife. Christian churches in northwestern Europe often used willow branches in place of palms in the ceremonies on Palm Sunday.^[13]

Willow in human culture

The willow is a famous subject in many East Asian nations' cultures, particularly in paintings (pen and ink) from China and Japan.

A Gisaeng (Korean Geisha) named Hongrang, who lived in the middle of the Joseon Dynasty, wrote the poem "By the willow in the rain in the evening", which she gave to her parting lover (Choi Gyeong-chang).^[14] Hongrang wrote:

"...I will be the willow on your bedside."

Willow trees are also quite prevalent in folklore and myths.^[15][16] In English folklore, a willow tree is believed to be quite sinister, capable of uprooting itself and stalking travellers.

The Viminal hill, one of the Seven Hills Of Rome, derives it name from the Latin word for osier, viminia (pl.).

In literature

Hans Christian Andersen wrote a story called Under the Willow Tree (1853) in which children ask questions of a tree they call willow-father, paired with another entity called elder-mother.^[17]

The Wind in the Willows

Algernon Blackwood wrote a story called The Willows (1907) about two friends on a canoe trip down the Danube river who have a horrifying experience with the trees. This story was a personal favorite of H. P. Lovecraft.

Green Willow is a Japanese ghost story in which a young samurai falls in love with a woman called Green Willow who has a close spiritual connection with a willow tree.^[18] The Willow Wife is another, not dissimilar tale.^[19] Wisdom of the Willow Tree is an Osage Nation story in which a young man seeks answers from a Willow tree, addressing the tree in conversation as 'Grandfather'.^[20]

In J. K. Rowling's Harry Potter and the Chamber of Secrets, and Harry Potter and the Prisoner of Azkaban, there is an old tree on the school grounds of Hogwarts called the "Whomping Willow". It was planted in order to conceal a secret passageway that Professor Remus Lupin roamed through every full moon when he began his transformation into a werewolf.

In William Shakespeare's Hamlet, the character Ophelia climbed a willow tree when a branch broke and dropped her into the river below where she drowned. In Shakespeare's "Twelfth Night", Viola (disguised as Cesario) tells Olivia "Make me a willow-cabin at your gate/ And call upon my soul within the house." The willow here being an emblem of forsaken love. In Shakespeare's Othello, Desdemona's song before her death uses the willow imagery to highlight her lost love.

J. R. R. Tolkien's The Lord of the Rings also features a character known as Old Man Willow which traps some of Frodo's companions until they are rescued by Tom Bombadil.

In Persian literature, the recognized adjective for 'willow' is lunatic (مجنون), and lover (or lovers' heart) is compared to willow in many texts.

Pictures

Weeping willow (Salix × sepulcralis) in Auckland, New Zealand	Dwarf willow (Salix herbacea), Sweden	Willow catkin (Salix discolor)	Sallow catkin (Salix caprea)
Willow leaves (Salix × sepulcralis)	Willow tree in a painting by Chinese artist Li Di, 12th century, Song Dynasty.	Salix discolor used in a decorative arrangement outside a hotel in Boston, Massachusetts.	willow on a pond

Main Species

The genus "Salix" is made up of around 400 species^[2] of deciduous trees and shrubs,:

See also

• Aravah, the Hebrew name of the willow, for its ritual use during the Jewish Feast of Tabernacles
• List of Lepidoptera that feed on willows
• Rhabdophaga rosaria, a Willow gall

External links

• Salix alba at plants for a future
• Salix purpurea at plants for a future
• 1911 Encyclopaedia Britannica
• Salix caroliniana images at bioimages.vanderbilt.edu
• Salix nigra images at bioimages.vanderbilt.edu
• Weeping Willow - Salix alba Diagnostic photos, Morton Arboretum specimens
• Willow Cuttings

References

• Keeler, Harriet L. (1900). Our Native Trees and How to Identify Them. New York: Charles Scriber's Sons. pp. 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
• Sviatlana Trybush, Šárka Jahodová, William Macalpine and Angela Karp (2008), "A genetic study of a Salix germplasm resource reveals new insights into relationships among subgenera, sections and species", BioEnergy Research 1(1), pp 67 – 79 (link)