Propagator Carlos Magdalena, who works at the gardens' tropical nursery, is the first person to succeed in hybridising the two types since attempts began in 1852.
The new hybrid has been named Nymphaea 'Kew's Electric Indigo', to reflect its spectacularly bright blue petals.
Magdalena took pollen from a white form of night bloomer Nympaea lotus (subgenus Lotos) and placed it on the stigma of day bloomer N. 'Barre Hellquist' (subgenus Anecphya).
Three weeks later, a fruit burst revealing around 40 seeds. But germination proved difficult, with the first three seeds producing seedling plants which died soon after. "Despite this, I kept monitoring the seed bag to try to spot new germinations," said Magdalena.
A week later, a fourth seedling grew, developing leaves with large, reddish markings. "I started to suspect that I had a special one," Magdalena added.
Two and a half months after germinating, the water lily flower opened on 16 January.
"It appears to be a day flowerer like its mother N. 'Barre Hellquist'. It opens at around nine in the morning," said Magdalena.
"I have received great feedback from other breeders. One even said I am making history."
Magdalena will now register the new variety on the Water Gardeners International Registry of Waterlily Cultivars, which already includes six tropical water lilies bred and published by him last year.
Other botanic gardens will be sent the new variety when numbers are increased. This summer, Magdalena's 2008 varieties N. 'Kew's Kabuki', N. 'Kew's Perfect Stranger' and N. 'Barre Hellquist' will be displayed for the first time at Kew's Waterlily House.
- View: www.watergardenersinternational.org/journal/4- 1/carlos/gallery1.html