Police have launched an appeal to trace a rare plant that has been stolen from one of the greenhouses at Kew Gardens, south-west London.

A Nymphaea thermarum, the smallest water lily in the world and extinct in the wild, is believed to have been stolen between 8.30am and 2.55pm last Thursday at the Princess of Wales Conservatory at attraction, a Scotland Yard spokesman said.

Experts believe the culprits would have had to dig or pull up the plant from a shallow pond.

The plant was discovered in 1987 in just one location, Mashyuza in Rwanda. But it disappeared from there around two years ago because of the over-exploitation of a hot spring that kept the plants moist and at a constant temperature.

There are more than 50 of the water lilies at Kew, which is the only place in the world where they are regularly propagated in large numbers. There are a small number of the plants still kept in Germany.

Their leaves can be as small as a centimetre (0.4in) in diameter. Anyone with information regarding the theft is asked to contact police on 020 8721 5934