Clarence A. Ryan

Clarence A. Ryan (1931 – 2007), often known as Bud Ryan, was an American plant biochemist whose research revealed key molecular mechanisms underlying plant defense responses to herbivory. He spent most of his career at Washington State University, where his laboratory discovered the peptide signaling molecule systemin, the first plant peptide hormone shown to activate systemic defense responses. His work helped establish the role of peptide signals in plant defense and plant–insect interactions.

Ryan was elected to the United States National Academy of Sciences in recognition of his contributions to plant biochemistry and signaling.