Botanical research in the state of Colorado has identified 12 plant species that are listed by the U.S. Fish and Wildlife Service (USFWS) as threatened or endangered (USFWS 1993a); and an additional 388 plant species considered to be of special concern by the U.S. Forest Service (USFS), the Bureau of Land Management (BLM), the USFWS, and/or the Colorado Natural Heritage Program (CNHP 1996).

The Colorado Rare Plant Field Guide has been produced through the efforts of the Colorado Rare Plant Technical Committee, a committee representing government and private interests, and concerned with protecting Colorado's flora. The Committee anticipates that a field guide to Colorado's rarest plants will facilitate the collection of botanical data, be indispensable to the establishment of conservation priorities, and enable informed land management decisions.

This first edition of the guide provides a summary of 173 rare plant species known to occur in Colorado, including all listed threatened and endangered plant species, all species formerly recognized by the USFWS as category 1 and category 2 candidates for federal listing (USFWS 1993b), and all plant species listed by the BLM (BLM 1990a) and the USFS (USFS 1994) as sensitive. For each species, information is presented on nomenclature, look-alike species, phenology, distribution, habitat, and references. Photographs of the rare plants and their habitats are included, as well as technical botanical illustrations showing distinguishing characteristics. We also present tables that show species distributions according to USFS, BLM, and National Park Service (NPS) boundaries. The guide is arranged in a three ring binder, with each page, front and back, devoted to just one species. This format was chosen to facilitate future updates to the guide, and to allow users to organize the species in the guide in a way they find most useful.

Data acquired over more than fifteen years by the Colorado Natural Areas Program (CNAP), The Nature Conservancy (TNC), the Colorado Natural Heritage Program (CNHP), and numerous individuals through field research, herbarium research, published floras, and scientific literature were used to produce the species accounts. As new information on rare, threatened, and endangered species is acquired, these data should be submitted to CNHP at Colorado State University. The Colorado Natural Heritage Program serves as the central repository for information on rare species and natural communities in the state, and welcomes all editorial comments on the guide.