Most species are known aswillow, but some narrow-leaved shrub species are calledosier, and some broader-leaved species are referred to assallow (fromOld Englishsealh, related to theLatin wordsalix, willow).
Some willows (particularlyarctic andalpine species) are low-growing or creeping shrubs; for example, thedwarf willow (Salix herbacea) rarely exceeds 6 centimetres (2+1⁄2 in) in height, though it spreads widely across the ground.
At the base of thepetiole a pair ofstipules form. These may fall in spring, or last for much of the summer or even for more than one year (marcescence).
Willows all have abundant waterybarksap, which is heavily charged withsalicylic acid, soft, usually pliant, tough wood, slender branches, and large, fibrous, oftenstoloniferousroots. The roots are remarkable for their toughness, size, and tenacity to live, and roots readily sprout from aerial parts of the plant.[3]
All thebuds are lateral; no absolutely terminal bud is ever formed. The buds are covered by a single scale. Usually, the bud scale is fused into a cap-like shape, but in some species it wraps around and the edges overlap.[4]
The leaves are simple, feather-veined, and typically linear-lanceolate. Usually they are serrate, rounded at base, acute or acuminate. The leafpetioles are short, thestipules often very conspicuous, resembling tiny, round leaves, and sometimes remaining for half the summer. On some species, however, they are small, inconspicuous, and caducous (soon falling).
In color, the leaves show a great variety of greens, ranging from yellowish to bluish color.
Willows are among the earliest woody plants to leaf out in spring and the last to drop their leaves in autumn. In the northern hemisphere, leafout may occur as early as February depending on the climate and is stimulated by air temperature. If daytime highs reach 10 °C (50 °F) for a few consecutive days, a willow will attempt to put out leaves and flowers.
In the northern hemisphere, leaf drop in autumn occurs when day length shortens to approximately ten hours and 25 minutes, which varies by latitude (as early as the first week of October for boreal species such asS. alaxensis and as late as the third week of December for willows growing in far southern areas).
With the exception ofSalix martiana,[5] willows aredioecious, with male and femaleflowers appearing ascatkins on separate plants; the catkins are produced early in the spring, often before the leaves.
Thestaminate (male) flowers have neithercalyx norcorolla; they consist simply of stamens, varying in number from two to 10, 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 square, 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 latitudinally. The filaments are threadlike, usually pale brown, and often bald.
Thepistillate (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.
The scientific use of the genus nameSalix originates withCarl Linnaeus in 1753.[1] The modern concept oftypes did not exist at the time, so types for Linnaeus' genera had to be designated later.[6] Thetype species, i.e., the species on which the genus name is based, isSalix alba, based on a conserved type.[1]
Thegeneric nameSalix comes fromLatin and was already used by the Romans for various types of willow.[7] A theory is that the word is ultimately derived from aCeltic language,sal meaning 'near' andlis meaning 'water', alluding to their habitat.[8]
Willows are classified into subgenera though what they should be is in flux.[9] Morphological studies generally divide the species into 3 or 5 subgenera:Salix (though some split off subgeneraLongifoliae andProtitae),Chamaetia, andVetrix. Phylogenetic studies have suggested thatChamaetia andVetrix be in one clade.[9]
The oldest fossils of the genus are known from the earlyEocene of North America, with the earliest occurrences in Europe during the EarlyOligocene.[10]
The genusSalix is made up of around 350 species of deciduous trees andshrubs. They hybridise freely, and over 160 such hybrids have been named.[2]Examples of well-known willows include:[11]
Willows areshade tolerant and typically short-lived. They require disturbances to outcompete conifers or large deciduous species. The seeds are tiny, plentiful, carried by wind and water, and viable only for a few days; they require warm and moist conditions to take root. The plants can alsoreproduce vegetatively from decapitated stumps and branches.[12]
Willows produce a modest amount ofnectar from which bees can makehoney, and are especially valued as a source of early pollen for bees.[13] Various animals browse the foliage[14] or shelter amongst the plants. Beavers use willows to build dams.[12] The trees are used as food by thelarvae of some species ofLepidoptera, such as themourning cloak butterfly.[15] Ants, such aswood ants, are common on willows inhabited byaphids, coming to collect aphidhoneydew, as sometimes dowasps.
Willow species are hosts to more than a hundred aphid species, belonging toChaitophorus and other genera,[16] forming large colonies to feed on plant juices, on the underside of leaves in particular.[17]Corythucha elegans, the willow lace bug, is a bug species in the familyTingidae found on willows in North America.Rhabdophaga rosaria is a type of gall found on willows.
Rust, caused by fungi of genusMelampsora, is known to damage leaves of willows, covering them with orange spots.[18]
A small number of willow species were widely planted in Australia, notably aserosion-control measures along watercourses. They are now regarded as invasive weeds which occupy extensive areas across southern Australia and are considered 'Weeds of National Significance'. Many catchment management authorities are removing and replacing them with native trees.[19][20]
Almost all willows take root very readily fromcuttings or where broken branches lie on the ground (an exception is the peachleaf willow (Salix amygdaloides)). One famous example of such growth from cuttings involves the poetAlexander Pope, who begged a twig from a parcel tied with twigs sent from Spain toLady Suffolk. This twig was planted and thrived, and legend has it that all of England's weeping willows are descended from this first one.[21][22]
Willows are extensively cultivated around the world.[23] They are used inhedges and landscaping.
The high end shopping district ofGinza inTokyo, Japan, has a long history of cultivating willow, and is well known for its willow lined streets.[24][25]
Weeping willow, an example of a hybrid between two types of willow
Willows are very cross-compatible, and numeroushybrids occur, both naturally and in cultivation. A well-knownornamental example is theweeping willow (Salix × sepulcralis), which is a hybrid of Peking willow (Salix babylonica) from China and white willow (Salix alba) from Europe. The widely planted Chinese willowSalix matsudana is now considered a synonym ofS. babylonica.
Numerous cultivars ofSalix have been developed and named over the centuries. New selections of cultivars with superior technical and ornamental characteristics have been chosen deliberately and applied to various purposes. Manycultivars and unmodified species ofSalix have gained theRoyal Horticultural Society'sAward of Garden Merit.[26] Most recently,Salix has become an important source for bioenergy production and for variousecosystem services.[citation needed]
TheQuinault people made the bark into a twine which sometimes served as harpoon line. The wood was used by some Native American tribes tostart fires by friction, the shoots toweave baskets, and both the branches and stems to build various items includingfishing weirs.[12]
InterpretingMesopotamiancuneiform texts is a challenge, especially when looking for something as specific as a species of plant being used to treat a recognisable condition. Some 5,000 medical prescriptions have been identified from Babylonian writings of the 7th to 3rd centuries BC, involving 1,300 drugs from 340 different plants. Whether any of these relate to willow is uncertain.[28] The seeds of the Haluppu-tree were recommended in the Sumerian narrative ofGilgameš, Enkidu and the Nether World as treatment for infertility, but the "Haluppu-tree" could have been oak, poplar or willow.[29]
The ancient EgyptianEbers Papyrus mentions willow (of uncertain species) in three remedies. One, as part of an elaborate recipe for a poultice to "make themet supple," which involved 36 other ingredients including "fruit of the dompalm, beans and amaa grains." The meaning ofmet is uncertain, but it may be something to do with the nervous system. The second is as part of a treatment for the "Great Debility," when "rush from the green willow tree" is combined with ass's semen, fresh bread, herbs of the field, figs, grapes and wine. Finally, it is used as a stiffening agent in a concoction of "fat flesh, figs, dates, incense, garlic and sweet beer" to put the heart into proper working order and make it take up nourishment.[30]
The Roman authorAulus Cornelius Celsus only mentions willow once: the leaves, pounded and boiled in vinegar, were to be used as treatment foruterine prolapse, but it is unclear what he considered the therapeutic action to be; it is unlikely to have been pain relief, as he recommendedcauterization in the following paragraph.[31][32]
Nicholas Culpeper, inThe Complete Herbal,[33] gives many uses for willow, including to staunch wounds, to "stay the heat of lust" in man or woman, and to provoke urine ("if stopped"), but he makes no mention of any supposed analgesic properties. His recommendation to use the burnt ashes of willow bark, mixed with vinegar, to "take away warts, corns, and superfluous flesh," seems to correspond with modern uses ofsalicylic acid.William Turner's account, written about 1597, focuses on the ability of the leaves and bark to "stay the spitting of blood, and all other fluxes of blood", if boiled in wine and drunk, but adds a treatment for fever, saying: "the green boughs with the leaves may very well be brought into chambers and set about the beds of those that be sick of fevers, for they do mightily cool the heat of the air, which thing is a wonderful refreshing to the sick patients."[34]
In 1763, ReverendEdward Stone, of Chipping Norton, Oxfordshire, England, sent a letter to theRoyal Society describing his experiments with powdered bark of white willow (Salix alba).[35] He had noticed the willow bark tasted bitter, like 'Peruvian Bark' (cinchona), which was used to treat fevers, and he speculated that the willow would have a similar effect. Over several years he tested it on as many as fifty patients and found it to be highly effective (especially when mixed with cinchona). Whether this was a real effect or not is unknown, but although Stone's remedy was experimented with by others at the time, it was never adopted by medical practitioners.[36] During theAmerican Civil War, Confederate forces also experimented with willow as a cure for malaria, without success.[37]
In his novelThe Mysterious Island (1875), the French novelistJules Verne outlined the state of scientific knowledge concerning medicinal uses of willow when one of his characters, Herbert (Harbert) Brown, was suffering from a fever induced by a bullet wound: "The bark of the willow has, indeed, been justly considered as asuccedaneum for Peruvian bark, as has also that of the horse-chestnut tree, the leaf of the holly, the snake-root, etc.", he wrote. In the story, Herbert is treated with powdered willow bark to no effect, and is saved when a supply of quinine is discovered.[38] It is clear in the novel that the causes of fevers were poorly understood, and there is no suggestion at all of any possible analgesic effect from the use of willow.
The first lasting evidence that salicylate, from willow and other plant species, might have real medicinal uses came in 1876, when the Scottish physicianThomas MacLagan experimented withsalicin as a treatment for acuterheumatism, with considerable success, as he reported inThe Lancet.[39] Meanwhile, German scientists tried salicylic acid in the form of sodium salicylate, a sodium salt, with less success and more severe side effects.[40][41] The treatment of rheumatic fever with salicin gradually gained some acceptance in medical circles.[42]
The discovery ofacetanilide, in the 1880s, gave rise to an 'acetylation' craze, where chemists experimented with adding an acetyl group to various aromatic organic compounds.[43] Back in 1853, chemistCharles Frédéric Gerhardt treated the medicine sodium salicylate withacetyl chloride to produceacetylsalicylic acid for the first time.[44] More than 40 years later in 1897,Felix Hoffmann created the same acid (in his case derived from theSpiraea plant),[45] which was found in 1899 to have ananalgesic effect. This acid was named "Aspirin" by Hoffmann's employerBayer AG. The discovery of aspirin is therefore only indirectly connected to willow.
In the late 1990s,Daniel Moerman reported many uses of willow by Native Americans. One modern field guide claims that Native Americans across the Americas relied on the willow as a staple of their medical treatments, using the bark to treat ailments such as sore throat and tuberculosis, and further alleging that "Several references mention chewing willow bark as an analgesic for headache and other pain, apparently presaging the development of aspirin in the late 1800s."[12]
Herbal uses of willow have continued into modern times.[46] In the early 20th century,Maud Grieve described using the bark and the powdered root of white willow (Salix alba) for itstonic, antiperiodic andastringent qualities and recommended its use in treating dyspepsia, worms, chronic diarrhoea and dysentery.[47] Like other herbalists, she makes no mention of it having any analgesic effect, despite widespread awareness of aspirin by this time, and she consideredtannin to be the active constituent.
It was long after the invention of aspirin that the idea emerged that willow bark is an effective painkiller.[48][49] It may often be based on the belief that willow actually contains aspirin.[50] Articles asserting that the ancients used willow for this purpose have been published in academic journals such as theBritish Journal of Haematology.[51] There are now many papers, books and articles repeating the claim that the ancients used willow for pain relief, and numerous willow-based products can be purchased for this purpose.[52] Modern research suggests that only the mildest analgesic effect could be derived from the use of willow extract, and even that may be due to flavonoids and polyphenols as much as salicylic acid.[53]
Cricket bats are traditionally made from willow wood.
Some of humans' earliest manufactured items may have been made from willow. A fishing net made from willow dates back to 8300 BC.[54]
Basic crafts, such as baskets, fish traps, wattlefences andwattle and daub house walls, were woven from osiers orwithies (rod-like willow shoots, often grown inpollards). One of the forms of Welshcoracle boat traditionally uses willow in the framework.
Thin or split willow rods can be woven intowicker, which has a long history. The relatively pliable willow is less likely to split while being woven than many other woods, and can be bent around sharp corners in basketry.
An aqueous extract of willow bark is used as a fungicide in the European Union. The willow bark extract is approved as a 'basic substance' product in the European Union and United Kingdom for the control of scab, leaf peach curl and powdery mildew on grapes, apples and peach crops.[55]
Male catkin ofSalix cinerea with beeWillow tree in spring, EnglandWillow tree withwoodbine honeysuckleArt installation "Sandworm" in the Wenduine Dunes, Belgium, made entirely out of willow
Warfare: Willow wood were used by the British to make parachute baskets throughoutWorld War II. Being light and strong, they could be made in any shape and bounced on impact. British production of willow baskets was about 2000 tonnes per year by some 630 manufacturers employing 7000 basket makers.[citation needed]Lawrence Ogilvie (a plant pathologist who had studied and written his 1920sCambridge University master's degree thesis about willow diseases) worked atLong Ashton Research Station, nearBristol and was much involved with these willows and their diseases.[58]
Dyeing: Willow is used to dye textiles, used to produce kimono. The kimono retailerGinza Motoji hosts annual willow dyeing lessons with fifth grade students ofTaimei Elementary School[59][60]
Art: Willow is used to makecharcoal (for drawing)[61] as well as living sculptures, woven from live willow rods into shapes such as domes and tunnels. Willow stems are used to weave baskets and three-dimensional sculptures of animals and other figures. Willow stems are also used to create garden features, such as decorative panels and obelisks.
Energy: There have been experiments or mathematical models in using willows forbiomass orbiofuel, inenergy forestry systems, due to its fast growth.[62][63] Programs in other countries are being developed through initiatives such as theWillow Biomass Project in the US, and the Energy Coppice Project in the UK.[64] Willow may also be grown to producecharcoal.
Environment: There has been research into possibly using willows for futurebiofiltration ofwastewater (i.e.phytoremediation andland reclamation), although this is not commercially viable.[65][66][67][68] They are used for streambank stabilisation (bioengineering),slope stabilisation,soilerosion control, shelterbelt andwindbreak, and wildlife habitat. Willows are often planted on the borders of streams so their interlacing roots may protect the bank against the action of the water. The roots are often larger than the stem which grows from them.
Food: Poor people at one time often ate willow catkins that had been cooked to form a mash.[13] The inner bark can be eaten raw or cooked, as can the young leaves and underground shoots.[14]
The willow is one of thefour species associated with the Jewish festival ofSukkot, or the Feast of Tabernacles, cited in Leviticus 23:40. Willow branches are used during the synagogue service onHoshana Rabbah, the seventh day of Sukkot.
InBuddhism, a willow branch is one of the chief attributes ofGuanyin, thebodhisattva of compassion.[citation needed] In traditional pictures of Guanyin, she is often shown seated on a rock with a willow branch in a vase of water at her side.
Orthodox churches often use willow branches in place of palms in the ceremonies onPalm Sunday.[69]
In China, some people carry willow branches with them on the day of their Tomb Sweeping orQingming Festival. Willow branches are also put up on gates and/or front doors, which they believe help ward off the evil spirits that wander on Qingming. Legend states that on Qingming Festival, the ruler of the underworld allows the spirits of the dead to return to earth. Since their presence may not always be welcome, willow branches keep them away.[70]Taoistwitches use a small carving made from willow wood for communicating with the spirits of the dead. The image is sent to the nether world, where the disembodied spirit is deemed to enter it, and give the desired information to surviving relatives on its return.[71] The willow is a famous subject in many East Asian nations' cultures, particularly in pen and ink paintings from China and Japan.
Agisaeng (Koreancourtesan) named Hongrang, who lived in the middle of theJoseon Dynasty, wrote the poem "By the willow in the rain in the evening", which she gave to her parting lover (Choi Gyeong-chang).[72] Hongrang wrote:
... I will be the willow on your bedside.
In Japanese tradition, the willow is associated with ghosts. It is popularly supposed that a ghost will appear where a willow grows. Willow trees are also quite prevalent in folklore and myths.[73][74]
In English folklore, a willow tree is believed to be quite sinister, capable of uprooting itself andstalking travellers.[75]
The Viminal Hill, one of theSeven Hills of Rome, derives its name from the Latin word for osier,viminia (pl.).
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".[76]
"Green Willow" is aJapanese 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.[77] "The Willow Wife" is another, not dissimilar tale.[78] "Wisdom of the Willow Tree" is anOsage Nation story in which a young man seeks answers from a willow tree, addressing the tree in conversation as 'Grandfather'.[79]
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