The hoodia cactus in question has been used for thousands of years by southern Africa's San Bushmen to dampen their appetites during long treks through the harsh Kalahari desert and holds the key to potentially lucrative anti-obesity drugs.
The Convention on International Trade in Endangered Species (CITES) listed the hoodia plant in its Appendix II - which will regulate global trade in the species - at the behest of South Africa, Namibia and Botswana.
It also adopted a Chinese and United States proposal to put Asian yew trees, which provide the compound for one of the world's top-selling chemotherapy drugs, in the same appendix.
That will give added protection to plants which could save untold human lives while earning billions of dollars for big drug companies.
The proposals will be raised again during the plenary session next week, but are almost certain to pass because they have strong support.
South Africa's Council for Scientific and Industrial Research (CSIR) has patented the chemical entity extracted from hoodia and licensed British drugs-from-plants firm Phytopharm Plc to develop the plant's commercial potential.
Phytopharm said in July it welcomed moves to protect hoodia from illegal cultivation.
"We're very pleased it went through," said John Donaldson of the South African delegation, saying it would help ensure that hoodia is used in a sustainable manner.
"We would like pharmaceutical companies to produce finished products in the three countries," he said, adding that there were structures in place to ensure that the San Bushmen derived benefits from the product.
VALUABLE BUT FRAGILE YEW
For years Chinese herbalists have used trees of the taxus species, also known as yew trees, to treat common ailments. In the late 1960s, scientists in North Carolina found that extract of yew bark fought tumours. In the early 1990s, the U.S. government approved the use of paclitaxel, also known as taxol, by drug company Bristol-Myers Squibb for chemotherapy.
Taxol, whose patent expired in the United States in 2001, is one of the best-selling drugs for treating a variety of cancers.
In 2003, drug firms sold more than $4 billion worth of products with taxol and other drugs derived from yew trees known as taxanes.
But conservationists say the various taxus species are under threat from illegal harvesting and habitat destruction in China.
"This is a win for conservation as well as for trade," Craig Manson, the head of the U.S. delegation, told Reuters.
"It ensures the products come from legal and sustainable resources. And it's important to preserve the species because it has a great impact on the lives of many people," he said.
CITES also agreed to regulate global trade in around 30 species of ramin, a tropical hardwood in huge demand for furniture production.
Illegal harvesting and over-exploitation of the species is one of many threats to one of humanity's closest living relatives, the highly endangered orang-utan.