American rarity. A map ranks U.S. areas according to how rare or irreplaceable their species are.

New Book Finds One Nation, Many Species

WASHINGTON, D.C.--Two conservation groups today released the most comprehensive look yet at the United States' creatures, plants, and habitats. From sea to shining sea (as well as Hawaii and Alaska), the country holds at least 200,000 species--double previous tallies. But up to one-third of them are threatened, mainly by loss of habitat, and 500 have gone extinct during the last 150 to 200 years or haven't been spotted for many years.

The data are published in a synthesis of 25 years' worth of state biodiversity inventories by The Nature Conservancy, the largest private U.S. conservation group, and a sister nonprofit, the Association for Biodiversity Information. The groups' scientists also surveyed systematists to fill out the species lists and drew on expert advice to create a new list of endangered species that includes species that haven't wound through the red tape to gain federal endangered status. In a richly illustrated, 400-page tome, Precious Heritage: The Status of Biodiversity in the United States, published by Oxford University Press, the groups present what conservation biologist Peter Kareiva of the National Oceanic and Atmospheric Administration calls "the most extraordinary assemblage of biodiversity data ever published."

Besides listing species, the book includes a first-ever map showing "hotspots" of species richness and rarity. To produce it, researchers calculated how biologically unique areas are, based on distribution data for 2800 at-risk species. Where can biological treasure be found? The southern Appalachian mountains, Hawaii, and California rank high, with "secondary hotspots" in such areas as Big Bend in Texas. Other fun facts: The United States has a wider array of ecological regions, such as tundra and desert, than any other country, and the world's richest collections of freshwater mussels and salamanders.