Willow catkins suggesting that despite the sub-zero temperatures spring is on its way?
Willows, sallows, and osiers form the genus Salix, around 400 species2 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 (derived from 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.
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. 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.
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.
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.
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 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.45
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.67
The leaves and bark of the willow tree have been mentioned in ancient texts from Assyria, Sumer and Egypt8 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).
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.
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.
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.10Large scale projects to support willow as an energy crop are already at commercial scale in Sweden11 , 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.
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.
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.