General description: Perennial forb with a basal rosette and a long branching, woody taproot. The linear leaves are bright green to grey-green, moderately thick and stiff, and irregularly dentate. The petals are reddish-orange before blooming, turning yellow with flowering (Denver Botanic Gardens 2008). The hypanthium is prolonged beyond the ovary as a slender tube.  Dehiscent capsule is 4-winged; capsule wings are 2-5 mm wide (Spackman et al. 1997).

Look Alikes: Oenothera flava taproot is fleshy and stout, and capsule wings are 1-2 mm wide (Spackman et al. 1997).

Phenology: Flowers in late May-June. Flowers open in the evening, and close by mid-morning (Spackman et al. 1997).

Restricted to sandy, gravelly and rocky soils, in seasonally wet areas; in meadows, depressions, or along arroyos in mixed conifer forest to sagebrush scrub (Wagner 1981). This species occurs in short outcrops or "rock reefs", drainages, and gullies (pers. comm. Densie Culver 2014).

Elevation Range: 5,298 - 9,108 feet (1,615 - 2,776 meters)

Colorado endemic: No
Global range: Restricted to Moffat County, Colorado and Daggett, Uintah, and Duchesne counties, Utah; Duchesne County, UT has just one occurrence. The Center for Native Ecosystems and Colorado Native Plant Society (2006) describe the range as "in the vicinity of the Flaming Gorge National Recreation Area and around Diamond Mountain, Cold Spring Mountain, and Douglas Mountain at the eastern end of the Uinta Mountains. It has been found as far west as Burnt Mill Spring, northwest of Roosevelt, and as far east as Boone Draw, below Sand Wash Basin in Moffat County, Colorado... The Uinta Mountains are relatively isolated from other mountain environments with similar elevational characteristics, and this isolation likely sets a natural limit on the geographic distribution." Range extent is approximately 5000 - 5500 square km when calculated using GIS tools.
State range: Known from Moffat County in Colorado. Estimated range in Colorado is 1523 square kilometers (588 square miles), calculated in GIS by drawing a minimum convex polygon around the known occurrences (calculated by the Colorado Natural Heritage Program in 2008). Also known from Utah.

The primary threat at this time is considered to be hydrologic alteration (Rondeau et al. 2011). It is not known if all of the occurrences are or are not threatened by these activities. Mesic areas and ephemeral creek bottoms in which this species occurs are often degraded by domestic livestock. Hydrologic alterations associated with livestock grazing (e.g. expansion of seasonal ponds/depressions) and associated trampling are potential threats to the species. As a species/habitat sensitive to decreased precipitation levels, Oenothera acutissima may be particularly vulnerable to climate change. This species occurs primarily on BLM and private land with no special protection status. Additionally, there is oil and gas development in the area, which could impact the plants.