Fifth of plants in danger of extinction new report suggests
One-fifth of the world's plants - the foundation of life on Earth - are at risk of extinction, a study concludes.
Researchers have sampled almost 4,000 species, and conclude that 22% should be classified as "threatened" - the same alarming rate as for mammals.
A further 33% of species were too poorly understood to be assessed.
The analysis comes from the Royal Botanic Gardens at Kew, the Natural History Museum and International Union for the Conservation of Nature (IUCN).
David Shukman reports.