Fears for 22% of world's plant species

One plant species in four could be endangered, according to scientists today.

Two US researchers report in the journal Science that at least 22% of plant species on Earth may be at risk of extinction. Plants are the makers of the world, producing oxygen, and converting the sun's energy into food, fuel, and shelter for the rest of creation.

They are the source of building materials, coal, toxins, narcotics, dyes, paper and fabric.

More than a quarter of all prescribed drugs are based on plants, and every year thousands of species are screened for potentially valuable pharmaceuticals.

Worldwide there could be up to 400,000 species of flowering plants. But the growth of humanity - the global population has doubled in fewer than 50 years - has put many at risk. For more than 10 years, botanists have assumed that about 13% of flowering plants face some danger of extinction.

Peter Jorgensen of the Missouri Botanic Garden, in St Louis in Missouri, and Nigel Pitman, of Duke University in Durham in North Carolina, examined patterns of threat in the places with the most variety and the fewest botanists - the tropics.

The pair looked at the data from 189 countries, examining the hazards to plants endemic to those nations. They calculated that the global proportion of threatened species is at least 22%, and could be 47%.

This discovery is in line with other, smaller studies. A team from Kew in London reported that of 162 cacti in the dry lands of Brazil, 64 were threatened. One conservation study found that 83% of plant species endemic to Ecuador were threatened.

The research has been greeted with alarm in Britain. "We have suspected that our existing estimates of the number of threatened plants are too low," said John Lawton, chief of Britain's natural environment research council. "It is good to have this more accurate assessment. But it just emphasises that we have a really urgent problem on our hands, and we must not delay taking action."

Peter Crane, director of the Royal Botanic Gardens at Kew, said that some countries had been able to assess only a tiny percent of their flora. Brazil reported that 2.4% of the plant species in its forests and savannahs were at risk.

"But that was more or less equivalent to the number that had been assessed. For some plant groups, studied at Kew, at least 50% of the Brazilian species are considered to be threatened."