The first comprehensive global study of the major plant families, released around the world last week, warns that more than one in 10 of the world's plant species are on the brink of extinction. A 15-year collaboration involving hundreds of researchers worldwide has found that 34,000 species--out of an estimated total of 270,000--are at risk.

The new Threatened Plants Report, known as the "red list" of the World Conservation Union, relates that the highest numbers of known endangered species are in the United States, Australia, South Africa, Turkey, and Mexico. Some families are in a particularly bad way: A third of lily species and 15 of 20 yew species could soon disappear. An "appalling" 29% of plant species in the United States are in peril, says John Sawhill, director of the U.S. Nature Conservancy. Close to one-third of members of the palm family are in trouble, as are one-third of a family of important timber trees in Southeast Asia, the Dipterocarpacae.

There are still huge gaps in the picture. Researchers have surveyed only about half the plant species thought to exist, and data in some regions--particularly Asia, South America, and Africa--are seriously lacking. "As information increases, the situation will likely be shown to be worse," says Harriett Gillett, one of the report's authors. Officials hope the new list will push countries into beefing up plant conservation plans.