Up, up and away: Dandelions use upward winds to spread seeds

Chris Roh '12 became interested in dandelions on walks with his toddler, picking the fluffy white spheres and blowing off their seeds. An aerospace engineer by training, Roh wondered about the fluid dynamics of this everyday activity. Why did some seeds release before others? And why did some seem to require much greater force to release?

New research by Roh, assistant professor of biological and environmental engineering in the College of Agriculture and Life Sciences, and his colleagues has uncovered the basic structural mechanics of how dandelions release and retain their seeds, opening new research pathways to understand plant evolution and seed dispersal in other wind-dispersed plants, such as lettuce and cotton.

In a new paper published Sept. 10 in the Journal of the Royal Society Interface, Roh and his co-authors report that dandelions respond to wind direction when releasing their seeds and have structures that make it harder for their seeds to release in unfavorable conditions. The first author of the paper is Jena Shields, a Ph.D. candidate in Roh's lab.

The moment dandelions release their seeds - called abscission - is crucial to the plant's reproductive success, Shields said. The new work builds on previous research that demonstrated wind-dispersed plants control abscission based on factors like humidity and wind strength.

"There's a growing understanding in the ecological field that the abscission process really affects dispersal of seeds and, therefore, plant reproductive success," Shields said. "We see dandelion seeds as a model species for a lot of wind-dispersed plants, so our hope is that understanding more about abscission in dandelions will help us understand wind-dispersed plants in general."

The team discovered that when seeds are being pushed toward the ground, they require almost five times as much force to release than when they're pushed upward. They also described the morphology of the very thin stems that connect dandelion seeds to the seed head; they discovered that the structure is asymmetrical, encouraging seeds to release in certain directions more readily than others. The researchers hypothesize that dandelions have evolved these structures to prevent their seeds from scattering too close by, creating competition that will harm themselves and their offspring.

Unlike many other fliers found in nature, like bees, insects or birds, these passive fliers only have control when they abscise, Roh said.

"How the seeds are attached to the parent plant, how they enable or prevent abscission based on environmental conditions - that moment is so important," Roh said. "It sets the trajectory and governs a lot of how far they will go and where they will land. We think this focus on the initial abscission process is probably one of the most crucial moments in their biology."

This basic discovery could have implications for understanding other wind-dispersed plants, for uncovering past and future plant evolution, and, perhaps most directly, for informing models of long-distance seed dispersal. Such models are used to predict how plant and disease populations may grow and spread, including the movement of invasive species to new locations and the spread of harmful plant diseases like wheat rust.

Additional co-authors are: Yukun Sun and Aspen Shih '26, doctoral and undergraduate students, respectively, in Roh's lab; Sridhar Ravi, associate professor at the University of New South Wales, Sydney; and Fiorella Ramirez-Esquivel, researcher at the University of New South Wales, Canberra.

The research was supported by the National Science Foundation, the Cornell Institute for Digital Agriculture, the National Institute of Food and Agriculture, the Office of Naval Research and the Asian Office of Aerospace Research and Development.

Krisy Gashler is a writer for the College of Agriculture and Life Sciences.