Waterwheels are under threat Barry Rice/CC BY-NC-SA 3.0

It’s an icon of evolution, but the waterwheel plant is facing extinction – and even its preservation in a seed bank looks doubtful.

The waterwheel plant (Aldrovanda vesiculosa) is the only aquatic plant known to use jaw-like snap traps to catch prey. It fascinated Charles Darwin, whose experiments were the first to show it was adapted for capturing water fleas and mosquito larvae.

The traps on the tips of its leaves are some of the fastest-moving appendages in the plant kingdom, taking just 10 miliseconds to snap shut when small invertebrates land on them.

Like many other carnivorous plants, the waterwheel has been heavily affected by habitat destruction and illegal collection. Its abundance has dropped by almost 90 per cent over the past century ­- despite it once being widespread across Australia, Africa, Asia and Europe.

And a study now says that a common way of conserving plants – seed banks – might not work for this species.

A team led by Adam Cross, a research associate at the University of Western Australia in Perth, collected seeds from wild and captive populations. The researchers then stored them for up to a year in different conditions, examining whether they germinated.

Some were buried in soil inside steel mesh bags at temperatures above freezing to simulate natural seed banks, whereas others were placed in hermetically sealed bags at -18 °C to replicate artificial indoor ones.

Struggle to survive

The team found that just 12 per cent of the seeds stored at above freezing temperatures were viable after a year. Most were destroyed by fungi.

“Our data suggests that in natural seed banks, A. vesiculosa seeds would be lost to fungal attack very rapidly – in between six and 12 months,” says Cross. “This means they are unlikely to persist between seasons.”

The reasons for the seeds’ resistance to storage could be down to a unique aspect of their morphology: their coats have a complex honeycomb-like arrangement that helps them to float. Cross thinks the honeycomb structure allows easy entry for the hyphal strands of fungi, which may explain why seeds are unusually susceptible to attack.

Meanwhile, all seeds stored at sub-zero temperatures for three months failed to germinate.

These findings mean that saving A. vesiculosa will not be easy, says Alastair Culham, a botanist at the University of Reading, UK. “The conservation will be expensive and technologically higher risk than conventional seed banking.”

So what are the alternatives?

In the long term, the most effective method of preservation will be habitat protection, says Cross. “We need to understand more about the species’ sensitivity to water quality to better understand the causes of its decline.”

Cryostorage of plants or embryos might also be an option, but this research is in its infancy, he says.

Journal reference: Botanical Journal of the Linnean Society, DOI: 10.1111/boj.12387

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