New research into the biomechanics of explosive seed dispersal in squirting cucumbers (Ecballium elaterium) reveals how these plants have adapted a suite of unique traits that help propel their high-speed seeds far and wide.
Seed dispersal comes in many forms, and much is known about animal, wind and water-assisted dispersal – but less is known about the self-propelled dispersal mechanisms of plants. One of these is the ballistic dispersal of the squirting cucumber, which uses high-pressure explosions to eject its seeds at high speed across large distances.
"Many factors have to interact perfectly to disperse the seeds in the most efficient way, while not destroying the whole plant too early," says Helen Gorges, a PhD student at the Department of Functional Morphology and Biomechanics in the Zoological Institute of Kiel University, Germany.
To reduce direct competition for space and resources between parent and offspring plants, there is an evolutionary drive for plants to disperse their seeds as far as they possibly can. The research conducted by Ms Gorges aimed to explore the mechanisms that control the cucumber's fruit during ripening and maximise its chances of successfully dispersing.
Ms Gorges and her team used microcomputed tomography to create a 3D-model of the whole fruit, as well as micro-CT imaging and high-speed videography to capture the exploding fruit in fine detail. "We recorded the explosion of the fruit with high-speed videos at 1,000 fps and 10,000 fps to calculate the speed of the seeds and the possible shooting distances," says Ms Gorges. "We also analysed pictures during the ripening of the fruits to measure the curvature of the fruit stem and the angle between fruit and stem."
Ms Gorges and her team found that the seeds can achieve speeds up to 29 miles per hour and reach shooting distances up to 12 metres. "It's super interesting to watch the explosions through high-speed recordings, as the explosions happen way too fast to see anything in real-time!" says Ms Gorges.
The experiments also revealed that the fruit stem straightens up during ripening, creating an average 53° angle that is close to the theoretical perfect angle of 50° that would maximise shooting distance.
Additionally, the team found that the seeds always exit the fruit facing the same way and produce a mucilaginous coat when they get wet, which becomes an adhesive when it dries and improves conditions for germination.
These findings have potential applications for bio-inspired launching systems as hydrogel-based actuators for medical tools and micro-robots. "There are also many applications in soft robotics, drug delivery systems and similar devices, where energy-efficient launching systems are desired," says Ms Gorges.
This research is being presented at the Society for Experimental Biology Annual Conference in Antwerp, Belgium on the 8th July 2025.
