LONDON • One in five types of plants worldwide is at risk of extinction from threats such as farming and logging that are wrecking many habitats, according to a report said to be the first global overview of plant life.

In total, 390,900 types of plants are known to science, from tiny orchids to giant sequoia trees, according to the State Of The World's Plants, written by 80 experts led by the Royal Botanic Gardens (RBG) at Kew, London.

And despite 21 per cent of all the species being threatened with extinction, the report also said new plants were still being discovered, such as a 1.5m-tall insect-eating plant on a mountaintop in Brazil last year.

Nonetheless, the experts said many parts of the world were suffering rapid change, such as from the felling of tropical forests to make way for farms and cities. Global warming was also among other man-made risks, it said.

"There's a huge change going on, mainly agricultural change and land for urbanisation," said Professor Kathy Willis, RBG Kew's director of science, yesterday. The report, meant as a first annual audit of the world's plants, omits plants such as algae and mosses.

Prof Willis said a rising world population of more than seven billion people needed food and places to live and that scientists should be pragmatic and help identify areas most in need of conservation.

The study said 31,000 plant species had documented uses such as in medicines, food or building materials. Little-known plants might have unknown benefits, such as resilience to diseases.

"If we completely clear the land and have a type of monoculture, what happens when a new plant disease emerges and wipes out the crop entirely?" asked RBG species conservation researcher Steve Bachman.

About 2,000 new types of plants were still being described every year. The one found in Brazil was the drosera magnifica, one of the largest-known carnivorous plants.

It was identified by a specialist in sundew plants who was reviewing photographs on Facebook taken by an orchid hunter.

The study found farming to be the biggest extinction threat, representing 31 per cent of the total risk to plants.

The threat of climate change and severe weather was estimated at 3.96 per cent, but Prof Willis said it may take until 2030 before the impact of climate change can really be measured.

"For most of the major groups of plants we're talking about, it takes at least 10, 20, 30 years before the next generation starts to produce flowers and pollen."

REUTERS, AGENCE FRANCE-PRESSE