A rare pygmy Rwandan water lily has been stolen from Kew Gardens.
Kew scientists are helping save the lily from extinction after it disappeared in the wild.
But a visitor has taken a nymphaea thermarum from a pond.
The plant is the world’s smallest water lily, about the size of a pound coin.
The lily went missing on 9 January from the Princess of Wales Conservatory.
Around 50 of the plants remain at Kew. Others are at the Bonn Botanic Gardens in Germany.
Director of horticulture Richard Barley said: "You can’t put a price on it by virtue of its rarity. It is a blow to morale. We take theft of our invaluable scientific collection of plants very seriously and this matter is with the police."