hybrid crack willow

Salix × fragilis is a medium-sized to large deciduous tree, which grows rapidly to 10–20 m (33–66 ft) (rarely to 29 m (95 ft)) tall, with a trunk up to 1 m (3.3 ft) diameter, often multi-trunked, and an irregular, often leaning crown. The bark is dark grey-brown, coarsely fissured in older trees. The lanceolate leaves are bright green, 9–15 cm long and 1.5–3 cm wide, with a finely serrated margin; they are very finely hairy at first in spring, but soon become hairless. The flowers are produced in catkins in early spring and are pollinated by insects. They are dioecious, with male and female catkins on separate trees. The male catkins are 4–6 cm long, the female catkins are the same length. The individual flowers have either one or two nectaries. In late spring, the fruit capsules release numerous small cotton-tufted seeds. These are easily distributed by wind and moving water and germinate immediately upon contact with the soil.

The plant is commonly called crack willow or brittle willow because it is highly susceptible to damage from wind, ice and snow. The name also derives from the twigs, which break off very easily and cleanly at the base with an audible crack. Broken twigs and branches can readily take root, enabling the species to colonise new areas when they fall into waterways and are carried some distance downstream. The plant is particularly adept at colonising new riverside sandbanks formed after floods. It also spreads by root suckers, forming pure 'groves'.

Salix × fragilis is cultivated as a fast-growing ornamental tree. The cultivar 'Russelliana' (syn. S. × fragilis var. russelliana) is by far the most common clone of crack willow in Great Britain and Ireland, very easily propagated by cuttings. It is a vigorous tree commonly reaching 20–25 m (66–82 ft) tall, with leaves up to 15 cm long. It is a female clone.