On Jan. 9, a thief stole a tiny water lily known as Nymphaea thermarum — the world’s smallest water lily and one of the planet’s rarest plants — from London’s Royal Botanic Gardens at Kew.

The thief is thought to have dug it from temperature-controlled mud in the gardens' lily pond.

Kew Gardens is one of only two places in the world that cultivate the special plant. It had only 30 of the plants on display and says the water lily is "priceless."

According to the gardens' website, the plant is so rare that it's never been given a common name, but it's unofficially referred to as the "pygmy Rwandan water lily."

The Nymphaea thermarum’s lily pads can measure as small as half an inch across, and its flower is about the size of a fingernail.

The plant was discovered at a hot spring in Rwanda by botanist Eberhard Fischer in 1987, and the spring is the water lily's only known location in the wild.

Nymphaea thermarum disappeared from the hot spring in 2008, but botanists at Germany’s Bonn Botanic Garden brought it back from the brink of extinction. The facility had several living samples and scientist were able to breed the water lily.

Kew Gardens horticulturalist Carlos Magdalena was finally able to grow the plant from its remaining seeds after numerous failed attempts.

He discovered that unlike other water lilies, Nymphaea thermarum grows in mud instead of water. He replicated its natural Rwandan hot spring habitat by heating damp mud to precisely 77 degrees Fahrenheit.

Until recently, the tiny plant could be found only at the Kew and Bonn botanical gardens, but some water lilies are now again growing in Rwanda. Still, they remain critically endangered.

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