Almost a third of cactuses are at risk of extinction because of threats including illegal trade and a spread of farms in arid areas, making the spiny plants among the most vulnerable species, scientists said on Monday.
"We were surprised to find that such a high proportion of cactus species are threatened ... and by the diversity of threats," lead author Barbara Goettsch told Reuters of the findings by an international team of researchers.
The study said 31 percent of 1,478 types of cactus assessed were at risk of extinction - a higher rate than the 25 percent of mammals or 12 percent of birds that are rated as vulnerable to dying out because of human pressures.
Cactuses range from a centimeter (0.4 inch) across to 19 meters (62 feet) high, and many are prized by collectors for brightly colored flowers that bloom unpredictably. An international treaty bans trade in many rare cactuses.
Inger Andersen, director general of the IUCN (International Union for Conservation of Nature), which oversees a Red List of threatened species, called the findings disturbing.
"They confirm that the scale of the illegal wildlife trade, including trade in plants, is much greater than we had previously thought," she said. Goettsch also works for the IUCN, based in Cambridge, England.
The study said that cattle ranching in arid lands, a spread of other farms and of roads and urban areas were also threatening cactus habitats in the Americas, from Chile and Uruguay to Mexico and the United States.
All species of cactus grow in the Americas except the mistletoe cactus found in Africa, Madagascar and Sri Lanka, the scientists wrote in the journal Nature Plants.
As a group of plants or animals, cactuses were the fifth most threatened behind cycads, amphibians, corals and conifers, the study said. Cycads are a type of fern-like plants.
PHOTO: Echinopsis cactus plants are seen at a plantation in San Ramon de Alajuela, 43 miles (70 km) north of San Jose July 1, 2010.
CREDIT: REUTERS/JUAN CARLOS ULATE.