"Over the centuries, [willow] has become identified with sadness, and become an emblem of grief, melancholy and lost love. In times gone by it was common for sprigs of willow to be worn as a symbol of grief." - Cassell Dictionary of Folklore.

"To wear the willow: To go into mourning,especially for a sweetheart or bride, to bewail a lost lover." - Brewer's Dictionary of Phrase & Fable.