Colorado
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Weber, W.A., and R.C. Wittmann. 1996a. Colorado flora: Eastern slope. Revised edition. Univ. Press of Colorado, Niwot, Colorado. 524 pp.
Colorado Native Plant Society. 1989. Rare plants of Colorado. Rocky Mountain Nature Association, Colorado Native Plant Society, Estes Park, Colorado. 73 pp.
Sivinski, R. 2004. Knowlton's Cactus (Pediocactus knowltonii): Progress Report. New Mexico Forestry Division; Santa Fe, New Mexico. 13 p.
Sivinski, R. 2002. Population characteristics of mancos milkvetch (Astragalus humillimus: Fabaceae) in San Juan County, New Mexico. New Mexico Forestry Division; Santa Fe, New Mexico. 10 p.
Heidel, B. and J. Handley. 2002. Draft: Bolophyta alpina (Wyoming feverfew) Conservation Assessment. Wyoming Natural Diversity Database. University of Wyoming. Laramie, Wyoming.
Weber, W.A., and R.C. Wittmann. 1996b. Colorado flora: Western slope. Univ. Press of Colorado, Niwot, Colorado. 496 pp.
Tuhy, J, P. Comer, G. Bell, D. Dorfman, B. Neely, M. Lammert, S. Silbert, J. Humke, L. Whitham, B. Cholvin, and B. Baker. 2002. A conservation assessment of the Colorado Plateau Ecoregion. The Nature Conservancy.. 435 p.
Peterson, S.J. 1982. Threatened and endangered plants of Colorado. U.S. Fish and Wildlife Service, Denver, CO. 35 pp.