Close-up video of fruit dehiscence and seed launch from Ruellia ciliatiflora

Seeds whirl furiously as they burst out of the fruits of the hairyflower wild petunia. Credit: E. S. Cooper et al./J. R. Soc. Interface

Biophysics

Wildflower seeds spin as fast as a dentist’s drill

No other known life form launches projectiles that rotate faster than this plant’s seeds.

A plant called the hairyflower wild petunia is known for shooting out its seeds at great speeds, which can top 15 metres per second. Now, physicists have shown that each seed spins at rates as high as 100,000 rotations per minute — as fast as some dentist’s drills, and faster than any other known natural projectile.

Dwight Whitaker at Pomona College in Claremont, California, and his team used high-speed cameras to record seeds bursting out of the fruits of the petunia (Ruellia ciliatiflora). The researchers observed that each disk-shaped seed rotates vertically, like a tiny bicycle wheel, rather than horizontally. But unlike a wheel, the seed travels forward while spinning backward.

This backward rotation stabilizes the seed, in the same way that a spinning top’s rotation keeps it upright. It also creates aerodynamic effects that increase stability and propel the seed upward. As a result, the plant can disperse its seeds as far as 7 metres away.