Oenothera acutissima W.L. Wagner:
United States (North America)

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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.

Oenothera acutissima most closely resembles O. flava, but can be distinguished by several factors. First, O. acutissima has a long, slender, branching taproot, while the taproot on O. flava is fleshy and stout. In addition, O. acutissima has larger flowers (petals 2.8-5 cm long) than O. flava (petals 1-3 cm long). O. acutissima also generally grows on shallower soils than O. flava. O. acutissima is also distinguished from similar species by its narrow, linear, irregularly toothed leaves; by its relatively small fruits (capsule), which is 14-18 (-22) mm long; and by its bright yellow flowers with reddish orange highlights, which fade to reddish-orange.

Comments: Grows along arroyos, in drainage channels, in depressions or shallow basins, in meadows or gravelly open areas, and in rock crevices. Restricted to sandy to gravelly soils, often growing among rocks; appears to be associated with a red quartzite of the Uinta Mountain Group. Seasonal (spring and early summer) or ephemeral water seems to be an important habitat component; this species tends to occupy locations that receive occasional flushings or spring runoff, such as the shallow channels at the bottom of seasonal or intermittent drainages. In many cases, the shallow drainage channels that support this species are fed by springs. A high percent bare ground and rock may also be important habitat elements; as drainage bottoms become more stable and achieve a higher percent ground cover, this species may be displaced by graminoids. These smaller-scale habitats are found within middle elevation coniferous forests (ponderosa and lodgepole pine), rocky mountain juniper-sagebrush communities, and sagebrush scrub. 1190 - 2600 m.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 6 - 80

Comments: 27 occurrences are known in total, approximately 15 in Colorado and 12 in Utah. 10 of these occurrences are currently ranked Historical (7 in Colorado and 3 in Utah), but most or all have this designation simply from not having been visited for 20 years or more; thus most or all of these "Historical" occurrences may be found to be extant upon re-survey. For example, a 2008 survey by the Denver Botanic Gardens found one "Historical" occurrence in Colorado to be thriving, with nearly 5,000 plants (Denver Botanic Gardens 2008). The Center for Native Ecosystems and Colorado Native Plant Society (2006) believe that "the plant's known range has been fairly thoroughly surveyed, and it seems unlikely many more occurrences will be discovered."

O. acutissima has large, strongly scented flowers and several observed pollinators, so some outcrossing likely occurs. However, it is also self-compatible. Additional field studies are needed to determine the relative contributions of self-pollination and outcrossing to the reproduction of this species (Raguso et al. 2007). It is also able to propagate vegetatively from its long lateral taproots (Center for Native Ecosystems and Colorado Native Plant Society 2006).

United States

Rounded National Status Rank: N2 - Imperiled

Rounded Global Status Rank: G2 - Imperiled

Reasons: Endemic to the mountains of northeastern Utah and adjacent Colorado; restricted to seasonally moist habitats with sandy to gravelly soil. Known from approximately 27 occurrences in total, although many have not been revisited recently. One large occurrence in Utah contains approximately 160,000 plants; most of the other occurrences have more moderate numbers, < 100 to several thousand individuals. Few or no occurrences are considered appropriately protected and managed at this time. Threats include livestock trampling and off- road vehicle use, which appear to affect nearly all occurrences to some degree.

Environmental Specificity: Very narrow to narrow.

Comments: Threats to this species' limited habitat include livestock trampling, expanding off- road vehicle (ORV) use, noxious weeds, road construction and maintenance, and, possibly, climate change. A few occurrences are seriously threatened by impacts such as heavy trampling or ORV damage, extensive water diversions and meadow channeling, or housing and infrastructure development; however, in other parts of the range, the rocky terrain and remote location may help to insulate populations. Nevertheless, most, perhaps all, occurrences are exposed to some degree of disturbance. Livestock trampling is the most significant threat; most to all sites are affected. Many of the springs that this species inhabits are used to supply water for livestock, exposing plants to trampling. In addition, a few sites are found adjacent to infrastructure such as stock ponds, corrals, and fence lines that concentrate cattle and exacerabate impacts. Cattle herbivory does not appear to be a serious threat at present, but this species is palatable to livestock and wildlife, and increases in grazing intensity may increase herbivory in the future. In addition, at least at two sites, significant herbivory by wild ungulates (mule deer and elk) has been noted (Raguso et al. 2007, Denver Botanic Gardens 2008). ORV use, increasing in this species' range, is allowed almost everywhere O. acutissima occurs, and ORV impacts have been noted at several sites. The wet soils inhabited by this species are easily rutted and displaced by tires. Invasive weeds such as cheatgrass (Bromus tectorum) are spreading throughout this species' range and have been documented at several occurrences. Livestock and ORVs often serve as vectors for these weeds. This species seems to prefer bare patches of soil or gravel within the stream channels it occupies, and there is concern that weed invasions could eliminate or alter this microhabitat, increasing substrate stability and percent ground cover. These alterations might allow other species to gain a competitive advantage over O. acutissima. Most occurrences are near roads, and some are directly bisected. Roads are a vector for ORVs, noxious weeds, and livestock, and road maintenance and road repair activities can directly damage plants. Roads are also a concern because of their impacts on site hydrology. Climate change is of particular concern for this species because it has a narrowly defined suitable habitat with a fairly specific hydrology, within a region that is experiencing increasing drought. Nevertheless, despite these factors, in 1988 Franklin commented that the species seemed relatively secure, at least within the Ashley National Forest (Franklin 1988 cited in Center for Native Ecosystems and Colorado Native Plant Society 2006).

Biological Research Needs: Research species' responses to anthropogenic disturbance.

Needs: Several dispersed sites need to be protected.

Comments: Wagner (1981) described large-flowered, self-compatible but presumably outcrossing plants endemic to the mountains of nw CO and ne UT as Oenothera acutissima, citing several vegetative and reproductive autapomorphies that distinguish it from O. flava. Subsequently, O. acutissima was treated as a variety of O. flava by Welsh (1986). A recent study of this and related taxa in Oenothera sect. Lavauxia found that this taxon was clearly distinct in terms of floral morphology and odor chemistry; combined with its edaphic specialization, autapomorphic vegetative characters, and the poor viability (and sterility) of artificial hybrids between O. acutissima and O. flava, these findings supported maintaining O. acutissima as a distinct species (Raguso et a. 2007).