As many as 10,000 out of the 50,000 known species of medicinal plants may be at risk, the study says.

The force for this is a fast-expanding demand for herbal remedies, a market that in North America and Western Europe has been growing by about 10 percent a year over the past decade and is now worth at least 11 billion poundsbillion euros, 19.9 billion dollars) a year, it says.

"Many of the plants are harvested by poor communities in India and China whose livelihoods will suffer if the plants die out," the report said.

The species most threatened include the African cherry, the bark of which is popular in Europe as a treatment for prostate enlargement.

Whole forests of this species have been felled to meet demand, and so many trees have been destroyed that the market has virtually collapsed.

The author of the study is Alan Hamilton, a plant specialist from the global environment network WWF who is also a member of the World Conservation Union's Medicinal Plants Specialist Group.

The study will be published later this year in a specialist journal, Biodiversity and Conservation, New Scientist said.

TERRA.WIRE