Waterwheel: Ten times faster than a Venus flytrap

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The stem of a light green plant with multiple branches consisting of small 'traps' Image copyright Plant Biomechanics Group Freiburg

Scientists have characterised the movement of the Venus flytrap’s aquatic cousin in detail for the first time.

The carnivorous Aldrovanda vesiculosa, also known as the waterwheel plant, snaps its “trap” shut ten times faster than the flytrap.

As it is quite rare in the wild, the plant’s mechanism has not previously been studied in great detail.

It is thought that the waterwheel and the flytrap may share a common ancestor.

However there is no fossil evidence for what this ancestor might have looked like.

“This is one of the main questions in the carnivorous plant community,” says Dr Simon Poppinga, an author on the study.

“Snap traps evolved only once in plants. There are two different mechanisms. Which one was first?”

A stressful life

The study, led by Anna Westermeier and Renate Sachse at the University of Freiburg, found that the waterwheel doesn’t use quite the same method as the flytrap.

Using a camera recording at 1000fps, researchers triggered the traps using an electrical stimulus.

“It’s very, very small and it’s very, very fast, and this puts you basically to the limits of optical resolution,” Westermeier told BBC News.

They realised that the plant’s traps are in a constant state of “pre-stress” – tensed to snap shut much like a bear trap – and when triggered by prey they quickly release and close.

The team noted that the action of the traps is due to a combination of hydraulics and the release of this pre-stress.

At just 2-4mm, the traps are about a tenth the size of a Venus flytrap’s, but they close in a remarkable 0.02 to 0.1 seconds.

The lobes or leaves of the waterwheel also do not change shape when they snap shut, but rather close like two halves of a mussel shell. The Venus flytrap flexes its leaves from flat to curved when enclosing its prey.

Image copyright Plant Biomechanics Group Freiburg
Image caption A single waterwheel plant may contain over 100 traps

Global neighbourhood

So where is the waterwheel likely to be dining near you?

According to Dr Poppinga, the plant is actually quite rare in the wild, even without the influence of anthropogenic climate change.

Despite this, its range is wide, and it is native to Europe, Africa, Asia and Australia.

“It’s actually a cosmopolitan,” explains Westermeier. “It grows anywhere there is water, if the temperatures are high enough.”

Favouring brackish, acidic environments like bogs, the plant is usually confined to small areas and can easily be eradicated in a region by fairly minor events.

Image copyright Plant Biomechanics Group Freiburg

It also looks much like an algae to the naked eye – the delicate structure of traps only revealing itself underneath a microscope.

Researchers hope to do further work investigating the waterwheel’s prey spectrum to determine what it feeds on.

It is currently thought to have a diet of small crustaceans like water fleas, possibly extending to tadpoles and small fish.

The findings were published in the Proceedings of the Royal Society.

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