Currently, the standard conservation assessment method is the one created by the International Union for the Conservation of Nature (IUCN) for its Red List, which since 1994 has used a scientifically rigorous, multicriteria process that assigns a species to such categories as "extinct," "least concern," "endangered," and "critically endangered."
Red List assessments have been completed for large groups of animal speciesbirds, mammals, and amphibiansbut so far, fewer than 15,000 plant species have been evaluated under the Red List process, in part because the procedure requires more data than is readily available for many species. According to Dr. Miller, there are approximately 300,000 known plant species, but many more remain to be discovered.
In designing a simpler process for evaluating plant species, Dr. Miller and his colleagues decided to assign species to only two categories: "At Risk" or "Not at Risk." The key criterion for determining a species' status was the size of its geographical range, or extent of occurrence (EOO). Under one of IUCN's criteria, a species with an EOO of more than 20,000 square kilometers (about 7,700 square miles, slightly smaller than the state of New Jersey) is considered not threatened, so that became the cutoff for determining whether a species would be categorized as At Risk or Not At Risk.
The Garden's scientists tested their approach by evaluating the 2,025 species of seed plants native to Puerto Rico, which was chosen because its plants are well documented in research collections. Data for the study came from the Global Biodiversity Information Facility, an international, open-access resource, and from the Garden's C.V. Starr Virtual Herbarium, a reposit
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The New York Botanical Garden