Well over half the threatened and endangered species listed with the U.S. Fish and Wildlife Service are plants. There are a total of 714 threatened and endangered flowering plants (713 U.S. species, 1 foreign species), 5 threatened and endangered conifers and cycads (3 U.S. species, 2 foreign species), 26 listed ferns and allied species (all U.S.), and 2 listed lichen species (both U.S.). Listed U.S. species are shown in Table 4.1, which lists flowering plants, and Table 4.2, which lists endangered conifers, ferns, and lichens. Because the status of most plant species has not been studied in detail, many more plants are probably in danger of extinction than appear on these lists.

Many factors contribute to the endangerment of plant species. Numerous species are the victims of habitat loss due to land and agricultural development. Others have declined due to pollution or habitat damage, or as...