Willow hybrids (Salix species) are bred as a cross between two or more true species of willow. The result is usually a large, fast-growing, upright tree rather than a shrub or weeping form. Many are bred to be sterile, as hybrids do not grow true from seed. All willow hybrids have many of the same characteristics, regardless of the parent species.
Hybrid willows can be quite tall. The specific size ranges according to the particular cultivar, but on average, they can reach a maximum height of 65 or more feet with a spread of 60 feet. Skyrise is a variety that grows to about 50 feet tall. Austree, another trademarked hybrid willow, is one of the largest with an average height of 70 feet.
Salix species range widely in the color of their leaves. Most are a medium shade of green on top with the same green or a paler color on the bottom. However, some are more gold than green, while others are a deeper, dark green. The leaves, which are rounded on one end and come to a point at the other, can vary in size depending on the cultivar. Gold panner is a willow hybrid bred to have golden leaves with red veins.
Willow hybrids, like the species, produce catkins. These are long, slender clusters of flowers that may dangle vertically from the branches in some cases. In other cases, they stand upright as small ovals. The clusters are noticeable, but the flowers themselves are very small, pale green or yellow, and insignificant, according to Ohio State University. The fruit takes the form of small, hollow pods filled with tiny, silky seeds that float on the wind.
Willow hybrids are bred to grow very fast. They are often marketed for use as fast-growing shade trees, privacy screens or windbreaks, according to Advanced Tree Technology. Some varieties, such as skyrise, can grow 5 feet or more per year. The fastest growth is seen during the first 4 years of life.