The award-winning plant that dines on rats and reptiles

A rat-eating plant has been declared a species previously unknown to science almost seven years after it was first exhibited at the Chelsea Flower Show.

The huge "Queen of Hearts" pitcher, one of the biggest carnivorous plants ever seen – with flowers stretching 2.5 metres across – took pride of place in a display at the world's premier flower show for five years and was seen by hundreds of thousands of visitors.

It helped growers to win four gold medals from the Royal Horticultural Society, but only now has it been recognised as a new species, despite being the most photographed pitcher plant in history.

The plant has a gaping opening through which insects, small mammals and reptiles plunge into a cauldron of hydrochloric acid and enzymes which break down their bodies for the nutrients. The contents are similar to that of the human stomach.

Nepethes robcantleyi was identified as new to science when, after being exhibited at Chelsea, a leaf and photographs were shown to Dr Martin Cheek, an expert in plant classification at the Royal Botanic Gardens in Kew, Surrey. "It is not normally how new species are discovered," said Dr Cheek. "It is very unconventional and a great surprise. But when I was presented with this material after the Chelsea Flower Show it didn't take me long to work out this is new to science. The plants are big and dramatic and are quite spectacular."

The pitcher is about 40cm long and 10cm wide, making it one of the biggest ever found. The flower is even bigger and stretches up to 2.5 metres (about 8ft) long and is thought to be the biggest belonging to a carnivorous plant.

The pitcher plant was filmed by Sir David Attenborough this year and is expected to feature in a new television series about Kew.

It was discovered by Rob Cantley, a former Hong Kong police officer who switched career to follow his passion for growing pitcher plants. He found two tattered flower heads in 1997 when he explored a remote forest which had just been felled in Mindanao, in the Philippines. He managed to collect some seeds and successfully propagated nine. Three plants flowered for the first time last year and, from the seeds they produced, he and his staff at Borneo Exotics, a pitcher plant business in Sri Lanka, were able to grow 3,000 seedlings, some of which are now at Kew. Despite follow-up visits to the area, the pitcher plant has never been seen in the wild again and, with its host forest destroyed, is believed to be extinct in the wild.

Mr Cantley said: "We have rats in the nursery and they are quite regularly caught by these plants. We have to fish them out. The plant can cope with them but we can't – the smell is disgusting.

"In the wild the plant would usually cling to trees and, as well as insects, it would probably normally catch tree shrews and small lizards."

Eden project: 'lethal' bracelets

The Eden Project has withdrawn from sale bracelets decorated with a potentially lethal tropical seed. The indoor rainforest in Cornwall had been selling the red seeded bracelets at its visitors' shop for a year before one of the centre's own horticulturalists spotted the poisonous seeds.

The bracelets contain a seed called abrus precatorius from Peru. David Rowe, a spokesman for the Eden Project, said: "We have identified the seeds as potentially dangerous. In an extreme case, if these seeds are chewed or ingested, it is very dangerous and potentially lethal."

The Eden Project asked buyers of the bracelets to return them.