Achievement

IGERT Trainee Dennis Evangelista and a Harvard botanist team discovered the mechanism of unique seed dispersal in a relative to geraniums. The plant flings its seeds up to half-meter away. Seeds then bury themselves by drilling into the ground. The twisting and untwisting is caused by changes in humidity. These behaviors are accomplished by dead tissue. Helical bristles, termed awns, attached to the seeds remain hygroscopically active. Dennis used a high-speed camera to record the catapult at 500 fps. Using engineering models, he estimated the energy stored in the coiling behavior and compared it to kinetic energy at launch. After removing losses due to drag, he found a match. Seeds disperse by using energy stored in dry awns acting as springs to fling the seeds. His model may help explain the invasive potential of this species and provides a framework for examining evolutionary tradeoffs in seed dispersal mechanisms. His discovery was featured in Science Now.