Horticulturist Carlos Magdalena points to an example of the rare and considered to be nearly extinct water lilly, Nymphaea thermarum. Royal Botanical Gardens Kew/AP Photo

By Timon Woodward and Jean Fievet

Scotland Yard detectives are hunting for clues after a priceless rare plant was stolen from the Royal Botanic Gardens, one of only a few known examples of the species.

The Nymphaea Thermarum, to give it its scientific name, is the smallest water lily in the world, and no longer grows in the wild. The plant that went missing last week was growing in an ornamental pond inside one of the conservatories at the west London establishment. It was saved from extinction by experts at Kew Garden in 2009 when Kew's top propagation horticulturist Carlos Magdalena managed to cultivate the species.

Botanists say they cannot put a value on an extinct species, but "millions is not an underestimate," according to Detective Constable Sam Johnston, who is leading the investigation.

"Police are appealing for information to trace a rare plant that has been stolen from the Royal Botanic Gardens at Kew," a spokesman for the Metropolitan Police said. "At some time between 8:30 a.m. and 2:55 p.m. on [Jan. 9] a Nymphaea Thermarum was stolen from the Princess of Wales Conservatory at the Royal Botanic Gardens Kew."

Kew Gardens is one of only two places in the world to cultivate the plant. Police believe it's likely that someone stole the plant on behalf of a collector.

Until a couple of years ago, the plant could only be found in one place in the world: Mashyuza in Rwanda.

The plant was one of about 30 on display in a shallow water lily pond at Kew.