It’s surprisingly challenging to disperse all of a dandelion’s fragile white seed tufts in any one direction, with some typically clinging around the stem regardless of the wind’s direction. The reasons behind a plant’s selective seed release have remained elusive.
Following nearly three years of experimentation and iteration, a research team from the U.S. and Australia has uncovered a unique structural feature that enables groups of seeds to capture upward air currents. This adaptation allows the plant to take advantage of unpredictable winds, explains fluid dynamicist Chris Roh from Cornell University.
Despite the absence of muscles to help ensure the best start for its offspring, the newly discovered structure provides the plant with significant force which minimizes the likelihood of seeds descending toward the ground, a fact highlighted in their findings published on September 10 in Journal of the Royal Society Interface.
The mechanism by which dandelion seeds navigate winds and remain airborne is already established. Just above the seed tuft, a swirling vortex of air resembles a “very plump doughnut with hardly a hole,” creating a low-pressure zone that keeps the tuft suspended, says Roh.
Regarding the initial inspiration for his research, Roh credits his 4-year-old daughter: “During our walks, when we blow on a dandelion, that curiosity sparked the whole idea,” he remarks.
As recalled by Cornell biophysicist Jena Shields, “Chris entered the lab, exclaiming, ‘Our fingers are FORCE SENSORS! Look at this dandelion!’”
By extracting ripe tufts at various angles, he demonstrated that tugging a seed upward is notably easier compared to pulling it downward. This led to his next task: “Now go measure it!”
Shields attached force sensors to individual dandelion tufts and found confirmation for their previous findings. Overall, removing the seeds at an upward angle required significantly less force than downward pulls. (The hardest method was pulling straight out, a result that’s stirring various hypotheses.) To her knowledge, these represent the first detailed measurements on the force needed to dislodge dandelion seeds.
Variations in ease of seed release likely arise from the microscopic structure at the connection between seed and the parent plant. Research led by biomechanist Sridhar Ravi at the University of New South Wales in Canberra revealed that seeds are attached by a slender, off-center strand, surrounded by a horseshoe-shaped shield. When wind or external forces attempt to pull a seed, this U-shaped structure stabilizes the seed until the force tilts it toward the lower opening; without this U’s support, the weight of the tuft can overwhelm the attachment. And off it goes!
Dandelions serve as “a fantastic example of scientific phenomena that have been right in front of us all along,” Shields expresses. She hopes that this exploration into dandelion biology encourages more people to ponder, “What makes this curious behavior happen?”
