The hybrid S. alba × S. fragilis. 

This hybrid needs to be carefully distinguished from its parents S. alba and S. fragilis. S. alba is here taken to include trees that have mature leaves that are distinctly and persistently hairy on at least one surface whereas S. ×rubens has mature leaves that are hairless or nearly so (many of the naturalised willows lie within this latter circumscription). S. ×rubens can also often be distinguished by its reddish twigs, leaves that are glossy above. S. fragilis differs in having extremely brittle twigs and larger, more leathery leaves with irregular teeth.

Source: Spencer, R. (1997). Salicaceae. In: Spencer, R.. Horticultural Flora of South-eastern Australia. Volume 2. Flowering plants. Dicotyledons. Part 1. The identification of garden and cultivated plants. University of New South Wales Press.