A study to be published later this year by the conservation organisation WWF warns that between 4000 and 10,000 plants may be at risk.


In an article published by New Scientist on Wednesday, study author Alan Hamilton said the market for herbal remedies had risen by 10% a year for the past decade in North America and Europe and had become an industry worth $20 billion at least.


The findings are based on an analysis of the number of species at risk on the World Conservation Union (IUCN) Red List of threatened plants.


Two-thirds of the 50,000 medicinal plants being used are harvested from the wild.


Hamilton, a member of the IUCN's Medicinal Plant Specialist Group, also contributed to a report which will be unveiled by the conservation organisation Plantlife International in mid-January.


Species under threat


Among the threatened plants are tetu lakha, a tree found in south India and Sri Lanka and used for anti-cancer drugs in Europe; an Indian root called saw-wort which is used for skin disorders and tendrilled fritillary, a Chinese plant used to treat respiratory infections.


"With demand and commercialisation growing fast, the future of the wild plants which have helped most of humanity for centuries is now more uncertain than it has ever been," Martin Harper, of Plantlife, told New Scientist.


The group, which says the problem has been looming for years, blames the herbal medicinal industry for not guaranteeing the sustainability of supplies.


"It is time for the industry to join forces with environmental organisations to ensure that herbal harvests have a sustainable future," Harper added.


Worldwide demand for herbal remedies is threatening natural habitats and endangering up to a fifth of wild medicinal plant species which are being harvested to extinction, a leading science magazine said on Wednesday.