Seeds from the plant join 1.7 billion already stored by Kew's Millennium Seed Bank partnership.
The seed bank partnership, at Wakehurst Place in West Sussex, involves more than 120 organisations in 54 countries and is now aiming to collect and conserve seeds from a quarter of the Earth's flowering plant species by 2020.
All the seeds are kept both in their country of origin and at Wakehurst, where they are stored in underground vaults that are kept at –20°C.
Kew director Professor Stephen Hopper said: "In the next phase we want to secure another 15 per cent, so by 2020 we will have a quarter of the world's seeds banked in both the country of origin and Wakehurst Place.
"And a major focus is going to be a considerable expansion in the sustainable use of seeds for human benefit.
"The thing that has changed over this 10-year period is a much more acute awareness of climate change as a threatening process, as well as the many others that impact on plant life.
"And the seed bank, as an insurance strategy, is a good, sensible way of keeping your options open for the future."
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