There are more than 400 types of willow tree known to exist throughout the world. There are also many hybrids and cross-bred varieties as well. Even with so many variations, every willow tree shares common attributes that are found across the entire spectrum of the group. Many willow trees are used for landscaping, shading and conservation properties. While some trees bear fruit, not all of the fruit is edible.
Willow trees are large water-loving trees found along riverbanks and other waterways. Willow trees can reach heights of up to 50 feet with branches spanning up to 30 feet. The bark is full of a watery sap that is charged with a salicylic acid. The wood is pliant and tough. The trunk and branches are slender giving the willow tree its slim tall look. Most types of willow trees are deciduous. The leaves are small, oval, elongated and serrated with rounded bases.
The more well-known types of willow tree are the Weeping Willow, Contorted Willow, Peking Willow, Goat Willow, Black Willow and Corkscrew Willow. There are also many hybrid variants as well including Cherry Willows. The Weeping Willow is the best known of the species; this tree is identified by the downward bow of the branches. The Black Willow is found in colder climates and can tolerate lower temperatures other willows cannot. The Corkscrew Willow is named for the twisted branches found on this tree; this is the type of willow tree favored by photographers. By contrast, the Contorted Willow displays different characteristics with each season including direction of branch growth and is best for limited growth areas. The Goat Willow is found in drier areas and is one of the smaller willow trees reaching only 15 to 30 feet in height. The Pussy Willow is well-known for its soft blossoms; this type of willow tree is good for areas with poor drainage where other trees have trouble growing.
Willow trees can grow in a variety of climates and locations. These trees are found in moist soils and cooler temperate areas of the Northern Hemisphere. Some trees, such as the White Willow, found in Europe, and the Peking Willow found in China, are region specific. Temperate areas of South America and Africa can support a few types of willow tree.
Willow trees have far-reaching roots which seek out water sources. Willow roots can grow from aerial parts of the tree and often become larger than the trunk of the tree. Willow trees are easily propagated from cuttings planted into the ground or even from broken branches left on the ground.
Willow trees have few problems with infections or disease. The most common causes of illness found in willow trees are Crown Gall, Willow Scab, Black Canker, Bagworm, Willow Leaf Beetle and Gypsy Moth. Crown Gall results from bacteria causing galls on the roots and stems; trees with numerous galls can become stunted, discolored and prone to secondary diseases that enter by way of the galls. Willow Scab is caused by a fungus and can quickly kill young willow trees; signs of this infection include green spore masses along the underside of leaves at the veins. Black Canker is a disease that usually accompanies Willow Scab. Willow trees with this infection show signs of dark brown spots on leaves and grayish white lesions with black borders on stems and twigs. If a willow tree suffers from both Willow Scab and Black Canker simultaneously it can die. Moth larvae, or caterpillar, infestation can also cause serious damage to willow trees. Both Gypsy Moth and Bagworm caterpillars feed on the leaves and twigs, causing defoliation that weakens the tree. A similar infestation is caused by the Willow Leaf Beetle; these insects attack willow tree leaves both in larvae and adult stages.
Willow trees can be used for a variety of purposes depending on the type of tree. The leaves and bark were used as medicinal remedies as far back as ancient Egypt and Greece according to Hippocrates. Native Americans used the salicylic acid as the predecessor to aspirin. Willow wood is also part of boxes, brooms, chairs and baskets. Recently willow trees have been grown as biofuel because of its high energy conversion rate and has also been used to make charcoal. The most natural use of willow trees is in conservation and soil retention along wetlands. The White Willow is used for paper while the Crack Willow is in some European countries to make purple dye for Easter eggs.