A plant which had not been seen in its native habitat for more than 70 years has been "brought back from the dead".
Simon Linington with the Belgium grass plants grown at Wakehurst
Botanists at Kew's country garden in Wakehurst Place, West Sussex, are growing Belgian grass from stored seed which was forgotten until recently.
The National Botanic Garden of Belgium asked for their help to germinate the last remaining seeds of the species.
Bromus bromoideus, once common in hayfields around Liege and Rocheford, declined rapidly from the early 1900s.
Changes in farming practices are thought to be largely to blame.
Only a quarter of the stored seeds found in Belgium were viable so some were sent to the Millennium Seed Bank at Wakehurst Place to increase their chances of germination.
"It was clear that I was probably looking at the last few seeds of this species in existence," said British botanist Dave Aplin, of the National Botanic Garden of Belgium.
"So some of the seeds were dispatched to Britain so that both institutes could try to germinate them."
Head curator at Wakehurst Place, Simon Linington, said the Belgian grass success showed that modern seed banking was a vital conservation tool.
The Millennium Seed Bank also stepped in to help reintroduce a related grass back into the wild in Oxfordshire.
Seed from Wakehurst Place, Ardingly, was used last summer to grow Bromus interruptus.
It flowered and produced sufficient seed for some to be sent back to the seed bank as a safeguard.