E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
An emblem of being forsaken. All round my hat I wear a green willow. So Shakespeare: I offered him my company to a willow-tree . to make him a garland, as being forsaken. (Much Ado About Nothing, ii. 1.) The very term weeping willow will suffice to account for its emblematical character.