LONDON One in five of the world's 380,000 plant species is threatened with extinction and human activity is doing most of the damage, according to a global study published on Wednesday.
Scientists from Britain's Botanic Gardens at Kew, London's Natural History Museum and the International Union for the Conservation of Nature (IUCN), found that more than 22 percent of species were endangered, critically endangered or vulnerable.
"The single greatest threat is conversion of natural habitats to agricultural use, directly impacting 33 percent of threatened species," the report said.
The findings were released ahead of a United Nations summit scheduled for mid-October in Nagoya, Japan where governments are due to set new targets for trying to conserve more of the world's plants and animals.
"We cannot sit back and watch plant species disappear -- plants are the basis of all life on earth, providing clean air, water, food and fuel. All animal and bird life depends on them and so do we," said Stephen Hopper, Kew's director.
The scientists used data analyzed in a five-year study to draw up what they called a "Sampled Red List Index for Plants" which will be added to a series of IUCN "Red Lists" that are designed to help monitor the changing status of the world's major groups of plants, fungi and animals.
As this was the first time a global analysis of the threat to the world's plants had been undertaken, the scientists said it would serve as a baseline to measure conservation efforts.
The study found that agriculture, development, logging, and using land for livestock were among the main reasons plant species were being threatened.
The worst-hit areas were tropical forests such as rainforests in Brazil, it said.
"Present day human activities are pushing more plants toward extinction, but if the world's governments take the right steps ... we do have the potential to safeguard plant life and the creatures that depend on it," said Steve Bachman, a plant conservation analyst at Kew.
The study included about 7,000 plant species drawn from five major groups.
Both common and rare plants species were assessed to try to give an accurate picture of how plants were faring around the world, the scientists said at a briefing for reporters.
Researchers studied a random sample of about 1,500 species from each group, since assessing the threat to all the world's estimated 380,000 plant species would be too enormous a task, they said.
By comparison to the vast plant world, experts estimate there are about 10,00 species of birds, 5,500 species of mammals and 6,300 species of amphibians.
"The diversity of plants underpins all life on earth, so it is sobering that our own species is threatening the survival of many thousands of plant species," said Neil Brummitt, a botanical diversity researcher at the Natural History Museum.
"We've set the baseline. Now we need to all work together to safeguard not only the future of plants but the future of ourselves."