Kew has a DNA bank with nearly 32,000 samples of plant DNA
Plants have never been as important to the environment, the director of Kew Gardens has said, ahead of the London conservation site's 250th anniversary.
They were vital to reduce the impact of climate change and "vast numbers of humans" needed them for medicine and food, Professor Stephen Hopper added.
Several major events will be held in 2009 to celebrate Kew's role as a world leader in plant science.
The first of these sees free public entry to the gardens on New Year's Day.
"We believe that at no other point in history have plants been so important to people," said Professor Hopper.
"They have importance as carbon sinks in a time of climate change.
"We have to care for what remains and address the serious business of repairing and restoring vegetation if we're going to have the buffers to climate variation that plant life offers."
There was an urgency to protect the plants which were essential to human welfare and quality of life, he added, as well as continuing to care for "green companions".
This year saw the opening of a walk through the trees at Kew Gardens
More than seven million preserved specimens of plants from around the world can be found in Kew's Herbarium.
An extension to this will open in 2009 to coincide with the 250th anniversary, helping Kew to cope with the 30,000 new specimens it receives each year.
A display of UK flowers such as orchids will also be held in the coming 12 months.
And there will be the Garden Photographer of the Year competition, plus the reopening of the Marianne North gallery, with a display of paintings by the Victorian artist.