By Alex Kirby
BBC News website environment correspondent
Some of the world's most endangered plants have a firmer grasp on survival than anyone had suspected until now.
The Philippine jade vine, Strongylodon macrobotrys, at risk from logging
A study by Botanic Gardens Conservation International says about 9,000 species which are threatened in the wild are in fact thriving in botanic gardens.
This is about a quarter of all the plants which are known to be at risk, but a fraction of the possible total.
Scientists say anything up to 100,000 species may disappear because of both habitat destruction and climate change.
Listing now possible
BGCI's survey, which took two years, involved the development of a new tool, the Plant Search Database.
This allows gardens for the first time to check what they hold in their collections against an international list of plants, recorded alongside their status in the Red Book of threatened species maintained by IUCN-The World Conservation Union.
Peter Wyse Jackson, secretary-general of BGCI, said: "This is an important step in helping to reverse the current extinction crisis that we face.
"BGCI is working with the botanic garden community to raise awareness about the plants they hold and the importance of these collections to future conservation efforts - they represent a living gene bank."
The giant Titan lily, Amorphophallus titanus, at Kew in London
The world's botanic gardens attract over 200 million visitors a year and are home to about 6.1 million living plants.
As well as acting as sanctuaries for plants, they help to educate visitors about the devastating impact humans are having on many species.
US scientists suggested two years ago that almost half of all plant species could be threatened with extinction.
Apart from habitat loss and climate change, threats include land-use changes, invasive alien species, and over-exploitation.
Images courtesy of Peter Wyse Jackson, Botanic Gardens Conservation International.