1997-06-13_REPORT - M1981302 (11)

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occurred at lower elevations. ' As the climate became drier, the boreal S. romanzoffiana retreated to higher elevations and S. maanicamoorum retreated to the eastern Great Plains. S. diluvialis persisted in warm wet situations, eventually becoming more limited to scattered areas of permanent moisture. Morphologically, S. diluvialis is intermediate between its putative progenitors. S. romanzoffiana is a montane plant of moist areas along streams and near lakes, rarely found below 2,438 meters (8,000 feet) in Colorado, and widely distributed across the northern part of the continent and in the western mountains to Arizona. S. romanzoffiana has a tight helix of inflated, ascending flowers around the spike, lateral appressed sepals, and a pandurate lip. S. maanicamoorum is a plains plant of moist areas, which has nodding, tubular flowers, with free and ascending lateral sepals, and an ovate to lanceolate lip. The center of distribution of S. maanicamoorum is in the Midwest, ranging from Texas to North Dakota. Disjunct populations in the Rio Grande Valley of New Mexico may indicate a once larger distribution for the species. S. diluvialis has flowers facing directly away from the stalk, neither ascending nor nodding, appressed or free lateral sepals, and a lip intermediate in shape between those of the putative parents. See Appendix I for further discussion on Ute ladies'-tresses taxonomy. C. Distribution Populations of S. diluvialis occur in relatively low elevation riparian, spring, and lakeside wetland meadows in three general areas of the interior western United States: near the base of the eastern slope of the Rocky Mountains in southeastern Wyoming and north-central and central Colorado; in the upper Colorado River basin, particularly in the Uinta Basin; and along the Wasatch Front and westward in the eastern Great Basin, in north-central and western Utah and extreme eastern Nevada. In 1994, the known range was expanded northward by discoveries in central Wyoming and western Montana. Figure I shows the distribution of the Ute ladies'-tresses orchid in the western United States excluding the Montana occurrence. The eastern most large populations are located in mesic riparian meadows of relict tall-grass prairie and irrigated pastures near South Boulder Creek at the southeast edge of Boulder, Boulder County, Colorado, and in mesic meadows in the riparian woodland understory along Clear Creek in adjacent Jefferson County, Colorado. The largest populations are managed by the City of Boulder Open Space Department and the City of Wheat Ridge, Colorado. A few plants are known from the lower reaches of Clear Creek Canyon, west of Golden, significantly upstream from the larger populations near Golden and Wheat Ridge. Smaller populations are currently known from private land along St. Vrain Creek, near Hygiene, Boulder County (discovered 1992) ; on property owned by Colorado State University near the Cache La Poudre River at the northwest edge of Fort Collins, Weld County (discovered 1993); and on state-owned land along Bear Creek, Goshen County, Wyoming (discovered 1993) . Historic collections were made in 1856 along the South Platte River, most likely near the mouth of Crow 2