Almost 600 plant species have been lost from the wild in the last 250 years, according to a comprehensive study.
The number is based on actual extinctions rather than estimates, and is twice that of all bird, mammal and amphibian extinctions combined.
Scientists say plant extinction is occurring up to 500 times faster than what would be expected naturally.
In May, a UN report estimated that one million animal and plant species were threatened with extinction.
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Researchers say their analysis of all documented plant extinctions in the world shows what lessons can be learned to stop future extinctions.
Most people can name a mammal or bird that has become extinct in recent centuries, but few could name an extinct plant, said Dr Aelys Humphreys of Stockholm University.
“This study is the first time we have an overview of what plants have already become extinct, where they have disappeared from and how quickly this is happening,” she added.