Willows, sallows, and osiers form the genus Salix, around 400 species 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. Some willows are low-growing
or creeping shrubs; for example, the dwarf willow rarely exceeds 6 cm in height, though
it spreads widely across the ground.
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 serrated
edges. Most species are deciduous; semievergreen willows; 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. Usually,
the bud scale is fused into a cap-like shape, but in some species it wraps around and the
edges overlap. 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, resembling tiny, round leaves, and sometimes remaining for half the
summer. On some species, however, they are small, inconspicuous, and caducous. 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 flowers are without either calyx
or corolla; 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 longitudinally. The filaments are threadlike,
usually pale brown, and often bald. The pistillate 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.
Cultivation Almost all willows take root very readily
from cuttings or where broken branches lie on the ground. The few exceptions include
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.
Willows are often planted on the borders of streams so 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. Hybrids
Willows are very cross-fertile, and numerous hybrids occur, both naturally and in cultivation.
A well-known ornamental example is the weeping willow, which is a hybrid of Peking willow
from China and white willow from Europe. The hybrid cultivar 'Boydii' has gained the
Royal Horticultural Society's Award of Garden Merit.
Ecological issues
Willows are used as food plants by the larvae of some Lepidoptera species, such as the Mourning
Cloak butterfly. Ants, such as wood ants, are common on willows inhabited by aphids,
coming to collect aphid honeydew, as sometimes do wasps.
A small number of willow species were widely planted in Australia, notably as erosion-control
measures along watercourses. They are now regarded as invasive weeds, and many catchment
management authorities are removing and replacing them with native trees.
Willow roots spread widely 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.
Pests and diseases Willow species are hosts to more than a hundred
aphid species, belonging to Chaitophorus and other genera, forming large colonies to feed
on plant juices, on the underside of leaves in particular. Rust, caused by fungi of genus
Melampsora, is known to damage leaves of willows, covering them with orange spots.
Uses Medicine
The leaves and bark of the willow tree have been mentioned in ancient texts from Assyria,
Sumer and Egypt as a remedy for aches and fever, and in Ancient Greece the physician
Hippocrates wrote about its medicinal properties in the fifth century BC. Native Americans
across the Americas relied on it as a staple of their medical treatments. It provides temporary
pain relief. Salicin is metabolized into salicylic acid in the human body, and is a precursor
of aspirin. In 1763, its medicinal properties were observed by the Reverend Edward Stone
in England. He notified the Royal Society, which 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 compound in its pure state. In 1897, Felix Hoffmann created a synthetically altered
version of salicin, 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 nonsteroidal anti-inflammatory drugs.
Willow has been listed as one of the 38 substances used to prepare Bach flower remedies, a kind
of alternative medicine promoted for its effect on health. However according to Cancer Research
UK, "there is no scientific evidence to prove that flower remedies can control, cure or
prevent any type of disease, including cancer". Manufacturing
Some of humans' earliest manufactured items may have been made from willow. A fishing
net made from willow dates back to 8300 BC. Basic crafts, such as baskets, fish traps,
wattle fences and wattle and daub house walls, were often woven from osiers. One of the forms
of Welsh coracle traditionally uses willow in the 'lats'. Thin or split willow rods can
be woven into wicker, which also 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. Willow wood is also used in the manufacture of boxes, brooms, cricket
bats, 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. Other
Agriculture: Willows produce a modest amount of nectar from which bees can make honey,
and are especially valued as a source of early pollen for bees. Poor people at one time often
ate willow catkins that had been cooked to form a mash.
Art: Willow is used to make charcoal 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 three-dimensional sculptures, such as animals
and figures. Willow stems are also used to create garden features, such as decorative
panels and obelisks. 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. Large-scale projects to support willow as
an energy crop are already at commercial scale in Sweden, and in other countries, others
are being developed through initiatives such as the Willow Biomass Project in the US and
the Energy Coppice Project in the UK. 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, slope stabilisation, soil erosion control, shelterbelt and windbreak,
soil building, soil reclamation, tree bog compost toilet, and wildlife habitat.
Religion: Willow is one of the "Four Species" used ritually during the Jewish holiday of
Sukkot. In Buddhism, a willow branch is one of the chief attributes of Kwan Yin, the bodhisattva
of compassion. Christian churches in northwestern Europe and Ukraine often used willow branches
in place of palms in the ceremonies on Palm Sunday.
Culture Culture: In China, some people carry willow
branches with them on the day of their Tomb Sweeping or Qingming 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. In traditional pictures of the
Goddess of Mercy Guanyin, she is often shown seated on a rock with a willow branch in a
vase of water at her side. The Goddess employs this mysterious water and the branch for putting
demons to flight. Taoist witches also 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. The willow is a famous subject in many East Asian nations' cultures,
particularly in pen and ink paintings from China and Japan.
A gisaeng 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. 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. 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.
Hans Christian Andersen wrote a story called "Under the Willow Tree" in which children
ask questions of a tree they call "willow-father", paired with another entity called "elder-mother".
Old Man Willow in J. R. R. Tolkien's legendarium, appearing in The Lord of the Rings.
"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. "The
Willow Wife" is another, not dissimilar tale. "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'. In "The Secret of Salix Babylonicus," set
in the Babylonian exile, the willow is portrayed benignly as a symbol of sympathy in grief
and perseverance in suffering, an upright character who shows solidarity with the exiles
and comes to express the spirit of the psalms.
Selected species
The genus Salix is made up of around 400 species 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 Willow Biomass Project
Willow water, using willow branches to grow roots of new cuttings - extracting biological
rooting hormones indolebutyric acid and salicylic acid
References
Bibliography Keeler, Harriet L.. Our Native Trees and How
to Identify Them. New York: Charles Scriber's Sons. Pages 393–395. ISBN 0-87338-838-0.
Newsholme, C.. Willows: The Genus Salix. ISBN 0-88192-565-9
Warren-Wren, S.C.. The Complete Book of Willows. ISBN 0-498-01262-X
Sviatlana Trybush, Šárka Jahodová, William Macalpine and Angela Karp.. A genetic study
of a Salix germplasm resource reveals new insights into relationships among subgenera,
sections and species BioEnergy Research. 1(1):67 – 79.
External links 1911 Encyclopaedia Britannica