Crack willow (Salix fragilis) is an invasive plant. It is a native of Eurasia.
The name derives from the twigs which break off very easily and cleanly at the base with an audible crack. The broken twigs and branches take root readily, enabling the species to colonize new areas, where the broken twigs fall into rivers and can be carried some distance downstream. It is particularly adept at colonizing new riverside sandbanks formed after floods and can form dense thickets several metres thick, with densely spaced stems that could be major impediments to access waterways .For more information about this plant pest, see the CABI data sheet.