Oenothera coloradensis ssp. coloradensis
Author: (Rydb.) Raven & Gregory


Colorado butterfly plant


Onagraceae (Evening Primrose Family)

Close up of Oenothera coloradensis by Georgia Doyle
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Close up of Oenothera coloradensis by Crystal Strouse
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Close up of Oenothera coloradensis by Crystal Strouse
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Taxonomic Comments

=Gaura neomexicana ssp. coloradensis

Ranks and Status

Global rank: G3T2
State rank: S1
Federal protection status: USFWS Threatened
State protection status: None

[+] Description and Phenology

Oenothera coloradensis by Katie M. Nichols
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General description: Short-lived perennial herb with one to several reddish, pubescent stems 50-80 cm tall. Lower leaves are lance-shaped, with smooth or wavy-toothed margins and average 5-10 cm long, while those higher on the stem are smaller and reduced in number. The inflorescence is located above the leaves and is flat-topped in bud. The multiple branches of the inflorescence elongate as the flowering season progresses. Usually only a few flowers are present at any time and are located between the floral buds and the mature fruits. Flowers have 4 white petals (turning pink with age) and are 1-1.5 cm wide. The hard, nut-like fruits are 4-angled and sessile (Fertig et al. 1994; Fertig 1994).

Look Alikes: Gaura parviflora is an annual with a narrow, elongate inflorescence at all stages, and with white flowers less than 3 mm long. Gaura coccinea is a low-growing perennial with leaves less than 3 mm long, and found in drier sites.

Phenology: Flowers June-September; fruiting July-October (Spackman et al. 1997).
 

[+] Habitat

Habitat of Oenothera coloradensis by Crystal Strouse
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Sub-irrigated, alluvial soils of drainage bottoms surrounded by mixed grass prairie (Spackman et al. 1997).  Frequently associated with species of Carex and Scirpus (Colorado Natural Heritage Program 1996; O'Kane 1988). 
 

Elevation Range: 4,859 - 6,378 feet (1,481 - 1,944 meters)

[+] Distribution

Distribution of Oenothera coloradensis in Colorado.
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Colorado endemic: No
Global range: The Colorado butterfly plant is currently known from approximately seventeen locations worldwide, all limited to a small geographic area [less than 60 miles X 60 miles] in southeastern Wyoming and adjacent western Nebraska and northeastern Colorado.
State range: Documented in Adams, Boulder, Douglas, Jefferson, Larimer and Weld counties in Colorado, however, several occurrences, including those in Boulder, Douglas, and portions of Larimer and Weld counties are now considered historical, and possibly extirpated. The current estimated range in Colorado is 2544 square kilometers, calculated in GIS by drawing a minimum convex polygon around the known occurrences. Imprecisely reported occurrences are not included. The species is also known from Wyoming and Nebraska.

 

[+] Threats and Management Issues

Summary results of an analysis of the status of Oenothera coloradensis based on several ranking factors. This species was concluded to be "weakly conserved”. From Rondeau et al. 2011.
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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. On agricultural lands, herbicide spraying, grazing by cattle and horses, haying and mowing, water development, conversion of rangeland to cultivation, competition from exotic plants, and loss of habitat to urban expansion have been cited as the main potential threats to the Colorado butterfly plant (Marriott 1987; Fertig 1994; Jennings et al. 1997). Oil and gas exploration is also a potential threat in portions of the species habitat. Within protected areas replacement of early successional vegetation by late seral species and high recreation use are the primary threats (Jennings et al. 1997).

The most serious threat on agricultural lands is probably the misuse of broadleaf herbicides for the control of Cirsium arvense, Euphorbia esula, and other exotic plants (Marriott 1987). Although competition from these species may have negative impacts on Oenothera populations, observations have indicated that the butterfly plant is highly susceptible to commonly used herbicides when they are applied indiscriminately. Alternative means of herbicide application and the use of biological control agents are currently being investigated in weed-infested areas of butterfly plant habitat on F. E. Warren Air Force Base (Floyd 1995, Munk et al. 2001, Burgess 2004).

Livestock grazing may be a threat at some sites, especially if animals are not rotated or if use is concentrated during the summer flowering period. Studies have shown that the Colorado butterfly plant may persist and thrive in habitats that are winter grazed or managed on a short-term rotation cycle (Mountain West Environmental Services 1985; Fertig 1994). Although reproductive individuals of Oenothera coloradensis ssp. coloradensis may be grazed (the plant appears to be quite palatable to a wide range of herbivores), the establishment and survival of seedlings and rosettes may be enhanced by the reduction of competing vegetative cover (Fertig 1994, 1996). Due to their low stature, rosettes do not appear to be regularly grazed (Mountain West Environmental Services 1985).

Mowing for hay production may be a threat if cutting is done before fruits are able to mature. Once the fruits have ripened, however, they are protected by a hard, woody fruit wall and are not damaged by cutting. The act of mowing in the fall may actually facilitate the dispersal of fruits (Jennings et al. 1997). Early season mowing (before the flowering stalks have elongated) may also be advantageous by reducing the cover of competing vegetation.

Construction of stock ponds and reservoirs, conversion of rangeland to crop cultivation, and the loss of habitat to residential and urban development are also important threats in agricultural areas. The city of Fort Collins contains areas of formerly suitable Colorado butterfly plant habitat that have been lost to urbanization. The protection or continued agricultural management of suitable private land habitat may be critical to the long-term survival of the species.

In non-agricultural areas, the main threat to Oenothera coloradensis ssp. coloradensis may be changes in habitat suitability resulting from natural succession. Without periodic disturbance events, the semi-open habitats preferred by this species may become choked by tall and dense growth of willows, graminoids, and exotic weeds (Fertig 1994). Natural disturbance events, such as flooding, fire, and ungulate grazing, may have been sufficient in the past to create favorable habitat conditions. In the absence of such events today, managed disturbance may be necessary to maintain and create areas of habitat (Fertig 1994; 1996).

In Colorado, one of the extant occurrences reports overgrazing and hydrologic alterations as potential threats. One of the populations which was not found in later searches had reported overgrazing and trampling as a threat.

[+] References

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    • Culver, D.R. and J.M. Lemly. 2013. Field Guide to Colorado's Wetland Plants; Identification, Ecology and Conservation. Colorado Natural Heritage Program, Colorado State University, Fort Collins, 694 pp.
    • Fertig, W. 1993. Census of Colorado butterfly plant (GAURA NEOMEXICANA SSP. COLORADENSIS) on F.E. Warren Air Force Base, 1993. Report prepared for the U.S. Air Force by the Wyoming Natural Diversity Database, Laramie, Wyoming. 30 pp.
    • Fertig, W. 1995. Census of Colorado butterfly plant (GAURA NEOMEXICANA SSP. COLORADENSIS) on F.E. Warren Air Force Base, 1994. Report prepared for the U.S. Air Force by the Wyoming Natural Diversity Database, Laramie, Wyoming. 37 pp.
    • Fertig, W. 1996. Census of Colorado butterfly plant (GAURA NEOMEXICANA SSP. COLORADENSIS) on F.E. Warren Air Force Base, 1995. Report prepared for the U.S. Air Force by the Wyoming Natural Diversity Database, Laramie, Wyoming. 38 pp.
    • Fertig, W. 1997. Census of Colorado butterfly plant (GAURA NEOMEXICANA SSP. COLORADENSIS) on F.E. Warren Air Force Base, 1996. Report prepared for the U.S. Air Force by the Wyoming Natural Diversity Database, Laramie, Wyoming. 40 pp.
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    • Marriott, H., and G. Jones. 1988. Preserve design package for a proposed Colorado butterfly plant Research Natural Area on F.E. Warren Air Force Base. Report prepared for the U.S. Air Force by the Wyoming Natural Diversity Database, Laramie, Wyoming. 32 pp. + app.
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Last Updated

2014-11-20