Imagine a plant that catapults its seeds with such force and precision it rivals the mechanics of modern engineering. Meet the squirting cucumber (Ecballium elaterium), a Mediterranean marvel that takes seed dispersal to new heights—literally. Its fruits, small and unassuming, pack an explosive punch, ejecting seeds at speeds of up to 20 meters per second and distances of up to 10 meters, which is 250 times the length of the fruit. This extraordinary process has puzzled scientists for generations, and now, a groundbreaking study published in the Proceedings of the National Academy of Sciences (PNAS) has revealed the secrets behind this botanical phenomenon.
Breaking down the explosion
In their paper, titled Uncovering the Mechanical Secrets of the Squirting Cucumber, researchers from the University of Oxford, including Lincoln Fellow Dr Dominic Vella, and the University of Manchester provide the first detailed explanation of how this plant achieves its explosive seed dispersal, and provides valuable insight into the evolutionary adaptations of this unique plant from inert to explosive fruits.
By integrating experiments, quantitative image analysis, high-speed videography and mathematical modelling, the team uncovered the precise series of the mechanical, hydraulic and ballistic features that turn the squirting cucumber’s fruit into a natural cannon.
Here’s how it works:
- Pressure Cooker: As the fruit ripens, it fills with mucilaginous fluid, building immense internal pressure. Think of a water balloon stretched to its limit.
- Ready, Aim: Just before ejection, the plant redistributes some of the fluid to its stem. This stiffens and elongates the stem, tilting the fruit to an optimal 45-degree angle for maximum launch efficiency. This redistribution of fluid from fruit back to stem and corresponding stiffening of the stem before the seed is launched appears to be a mechanism unique to this species.
- Fire: When the fruit finally detaches, the stem recoils, causing the fruit to spin and eject its seeds in a rapid burst. The process, lasting just 30 milliseconds, ensures that seeds are flung uniformly far and wide.
- Strategic Spread: The seeds don’t just fly—they’re launched with varying speeds and angles. The first seeds go the farthest, while the last ones land closer, creating a ring-shaped dispersal pattern that maximises the chances of survival.
Dominic Vella, a co-author on the paper, said: “The squirting cucumber’s scientific name (Ecballium) comes from the Greek term εκβάλλω (ekvállo), meaning ‘to expel’, and accurately describes what this fruit does to disperse its seeds. However, what we’d never guessed was how intricate the steps the plant goes through to achieve that efficiently would be – and many questions remain. In particular, how the plant ‘knows’ when it has reached the optimal launch angle is a fascinating question for future work and may provide new insights into how plants move water to effect shape changes.”
F. Box, D.E. Moulton, D. Vella, Y. Bhagotra, T. Lowe, A. Goriely, C.J. Thorogood, Uncovering the mechanical secrets of the squirting cucumber, Proc. Natl. Acad. Sci. U.S.A. 121 (50) e2410420121, https://doi.org/10.1073/pnas.2410420121 (2024).