Killer petunias and murderous potatoes

10 December 2009

Could petunias be killers? Or potatoes be murderous? Yes, according to new research into carnivorous plants, published in the Botanical Journal of the Linnean Society last week.

Scientists from the Natural History Museum and the Royal Botanic Gardens, Kew, say that carnivorous behaviour in plants is far more widespread than previously thought, with many common plants, such as petunias, part way to being ‘meat eaters’.

Pitcher plants are one of the 3 most well-known carnivorous plants

Pitcher plants are one of the 3 most well-known carnivorous plants

The team reviewed studies of different groups of plants - from the 3 carnivorous groups of sundews, pitcher plants and the famous venus fly traps that clearly trap, digest and absorb the remains of their prey, to other plants not traditionally thought of as carnivorous.

The Natural History Museum’s plant expert Maarten Christenhusz explains, ‘We assessed studies carried out to test for vegetable carnivory and concluded that there is a wide spectrum of murderous plants.’

Sliding scale of carnivory

The research highlights how it is no simple matter to categorise plants as either non-carnivorous and carnivorous plants.

Instead the team found that there is a ‘sliding scale’ of carnivory, with plants with less obvious carnivorous characteristics like petunias at one end, and real ‘meat eaters’ with active traps like the venus fly trap, at the other end.

Petunias and potatoes

Innocent-looking plants like petunias and potatoes have sticky hairs that may perform a more gruesome role. Passing insects get trapped in the hairs and some plant species have been shown to produce digestive enzymes that can absorb the remains of the unlucky insect.

The carniviorous bog plant, sundew

The carniviorous bog plant, sundew

This happens in flowering plants of the nightshade (Solanaceae) and sesame (Pedaliaceae) families, as well as in geraniums and passion flowers.

Others species produce the enzymes but have not been shown to digest the prey. And there are other examples of plants that absorb prey remains through their roots after the prey has fallen to the ground and been incorporated into the soil.

Murderous seeds

‘Some species, such as the shepherd’s purse, even have seeds that attract and poison soil life,’ says Christenhusz. ‘So the seedling has additional nutrients in the soil and it will not be predated on.’

Long-held fascination
Venus fly trap

Venus fly trap with a meal worm © wikipedia

People have long been fascinated by plants that devour animals. ‘Especially when larger prey is involved, like birds, frogs or rats,’ says Christenhusz.

The team had many stories and tales to explore, including Gothic horrors from Victorian times. More importantly, however, were some scientific studies from many years ago, such as those by Darwin.

‘Gruesome stories of man-eating plants were commonplace in Darwin’s time, but his book, Insectivorous Plants, changed the way science approached these ‘wonders of nature’.

Rat-eating plant

According to Christenhusz, despite recent reports of a plant large enough to consume rats, this behaviour is doubtful. ‘The chance that Nepenthes attenboroughii catches rats is quite unlikely. It will only consume rats if you put a dead rat in its pitcher.’

Although there is a wide variety of murderous plants, Christenhusz says that scientists have not yet found a plant that consumes anything larger than a small bird.

Bird-eating plants

Small birds need to beware in the Pacific and South America. The Pisonia plant, a tropical liana growing on Pacific islands, has sticky seeds that small birds get caught up in. ‘The seeds are so sticky that the bird gets entangled, cannot fly anymore and dies.’

'There is also a report of a deadly bromelia of the genus Puya in South America,' says Christenhusz. ‘It has inwardly curved spines, which birds use to build their nest in. 

'Unfortunate birds can get trapped and die, providing nutrients for the plants on these high Andean slopes. Researchers found an enormous amount of dead birds in just a few plants.

So, as this research highlights, there is a world of plants out there with differing levels of carnivory. And you may look at the humble potato and petunia in a different way from now on!

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