World’s Smallest Water Lily Debuts in Garden Pools

Barely the size of a penny, the flower of Nymphaea thermarum is easy to miss next to its showier cousins in the Missouri Botanical Garden aquatic plant pools. But this little water lily, on public display for the first time at the Garden, has quite an impressive backstory.

Nymphaea thermarum has small white flowers, less than half an inch across. The lily pads can be just as tiny, and the entire plant may only reach 7 to 8 inches in diameter. Compare that to the world’s largest water lily, Victoria amazonica, with leaves that can reach up to nine feet across. Indeed, an entire N. thermarum plant could conceivably fit within a single flower from V. amazonica.

Nymphaea thermarum isn’t just tiny, it’s also incredibly rare. The plant was discovered in 1987, and less than 30 years later it was considered extinct in the wild. The only known wild population was found near a hot spring in southwestern Rwanda. Over-exploitation of this water source caused the hot spring to dry up, wiping out the tiny water lily’s native habitat.

But this is where botanical gardens like ours come into play. Botanist Eberhard Fischer, who discovered the wild population, was able to bring several plants back to Bonn Botanical Garden in Germany. Horticulturists there and at Royal Botanic Garden Kew then began trying to solve the mystery of how to propagate it. And that was a much more difficult task than expected.

These two gardens were able to grow N. thermarum, but the plants were barely clinging to life and never reached maturity. Then in 2010, Kew propagation specialist Carlos Magdalena was able to solve the mystery using clues from the plant’s native habitat.

All other water lilies germinate underwater, but N. thermarum was different. It grew in wet mud near the hot spring, not fully submerged in water, meaning the seeds needed exposure to air and water. By adjusting the water level in relation to the loam soil and regulating the water temperature, Magdalena found the key to successfully cultivating N. thermarum.

Nymphaea thermarum blooms in the Garden greenhouse in 2018.

Magdalena’s breakthrough allowed Kew to propagate dozens of seeds, and sharing that critical information has allowed other botanical gardens to follow suit. The Missouri Botanical Garden received seed of N. thermarum in 2017 from Arnold Arboretum at Harvard University, which trace their genetics to the original plants brought to Bonn Botanical Garden.

Derek Lyle, Senior Manager of the Garden’s Nursery, was able to get the plant to flower in the greenhouse propagation pools in 2018. This year, two of the tiny water lilies were put on public display in the water lily pools outside the Linnean House.

Cassidy Moody — Senior Digital Media Specialist

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