‘Squirting cucumber’ may sound like a vulgar euphemism, but it’s truly one of the most remarkable species in the natural world.
The quirky plant, a relative of the edible cucumber, ejects its seeds at a whopping 44mph – even faster than the human ejaculate (around 28 miles per hour).
Now, a new study reveals how exactly the squirting cucumber – native to southern Europe and northern Africa – manages this awe-inspiring feat.
Scientists at the universities of Oxford and Manchester say the plant builds up pressure and stiffens to get the perfect angle for seed dispersal.
This increases chances of survival as the seeds are more likely to be transported to more favourable environments for growth.
Astonishing footage shows the 30-millisecond act – described as ‘one of the most rapid motions in the plant kingdom’ – slowed down 400 times.
‘For centuries people have asked how and why this extraordinary plant sends its seeds into the world in such a violent way, said study author Dr Chris Thorogood, head of science at Oxford Botanic Garden.
‘Now, as a team of biologists and mathematicians, we’ve finally begun to unravel this great botanical enigma.’
Officially called Ecballium elaterium, the squirting cucumber consists of an egg-shaped fruit attached to a long, thin stem.
When ripe, the fruit detaches from the stem and ejects seeds in a high-pressure jet of ‘mucilage’ – the thick gluey substance produced by nearly all plants.
Despite intriguing scientists for centuries, the exact mechanism of seed dispersal and its effect on subsequent generations remain poorly understood,’ the team say in their paper, published in PNAS.
To learn more, researchers at Oxford Botanic Garden filmed the plant’s moment of climax (the seed dispersal) with a high-speed camera, capturing up to 8,600 frames per second.
They also measured fruit and stem volume before and after dispersal, calculated its hardness, performed CT scans, and monitored the fruit with time-lapse photography in the days leading up to the big moment.
They then developed computer models to unravel the mechanics of the pressurised fruit, the stem and the trajectories of the seeds.
It showed the projectile launch – lasting just 30 milliseconds – causes the seeds to reach speeds of around 44 miles per hour (20 metres per second).
This is even faster than the human ejaculate – around 28 miles per hour!
The squirting cucumber’s seeds then land at distances of up to 32 feet (10 metres) away – around 250 times the length of the egg-shaped fruit.
The researchers found that the squirting cucumber goes through several phases as part of its dramatic expulsion, many of which pass sooner than a blink of the eye.
In the weeks leading up to the ‘ballistic ejection’, the egg-shaped fruit becomes more and more pressurised due to a build-up of its mucilaginous fluid.
In the days before dispersal, some of this fluid is redistributed from fruit to stem, making the stem longer, thicker, and stiffer (ooh matron!)
This causes the fruit to rotate from being nearly vertical to an angle close to 45 degrees, a key element needed for successful seed launch.
But, as the footage shows, it’s the separation of the fruit from the stem which may prove especially eye-watering for male viewers.
In the first hundreds of microseconds of ejection, the tip of the stem recoils away from the fruit, causing the fruit to counter-rotate in the opposite direction.
The seeds that get ejected the first are the fastest and hence travel further, while subsequent seeds land closer – simply because the pressure of the fruit capsule decreases as it empties its load.
As there are multiple fruits around the centre of the plant, the result is a wide distribution of seeds covering a ring-shaped area at a distance of up to 32 feet (10 metres) from the mother plant.
The team’s computer model also showed that if the stem were thicker and stiffer prior to climax, the seeds would be launched almost horizontally, since the fruit would rotate less during discharge.
Meanwhile, reducing the amount of fluid redistributed from the fruit to the stem resulted in an over-pressurised fruit, causing the seed to be ejected at higher speeds but at a nearly vertical launch angle.
In both cases, the seeds wouldn’t be expelled as far and fewer would be likely to survive, ultimately meaning less reproductive success.
The team say the seed projection method of the squirting cucumber has evolved over generations to become as effective as possible.
‘The redistribution of fluid from fruit back to stem and corresponding stiffening of the stem prior to seed ejection appears to be a mechanism unique to this species,’ they conclude.
‘Our comparative analysis has demonstrated that these mechanical details are critical to the successful dispersal of seeds and propagation of the plant to subsequent generations.’
According to Dr Thorogood, the ancient Greeks were aware of the squirting cucumber, which is inedible due to the toxic chemicals it contains.
The first observations are those made by Theophrastus, a philosopher who lived from 371 to around 287 BC, according to the academic.
