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Pale Evening-primrose - Oenothera pallida ssp. pallida
Other Names:
Oenothera pallida var. idahoensis
State Rank Reason (see State Rank above)
DRAFT: Requesting feedback on the 2026 revised rank, factors, and State Rank Reason outlined below and in the Conservation Status Rank Report.
Oenothera pallida ssp. pallida is extremely rare in Montana, where it occurs at the northern edge of its range in the Centennial Sandhills. The populations occur primarily on lands managed by the Bureau of Land Management and the U.S. Fish and Wildlife Service; these are in areas managed primarily for their conservation value as part of an Area of Critical Environmental Concern or as a Wildlife Refuge. Population levels are poorly documented with no recent estimates of population size available. The species' habitat is largely intact and in good condition though vegetation succession and dune stabilization may be reducing the amount of the early successional habitat that is preferred by the Evening-Primrose. No other direct threats to the species are known. Population trends are unknown because of the lack of survey and monitoring data.
Climate change may negatively affect this species over the next several decades. However, the timing and magnitude of potential impacts are largely unknown. Although climate change is listed as a potential threat to the species, it does not affect the overall threat rank or scoring, or the final subnational rank.
Survey and monitoring data are greatly needed to be able to more precisely determine population levels, assess condition and for assessing population trends.
General Description
Pale Evening-primrose is a rhizomatous perennial with whitish, peeling bark and erect or ascending, often branched stems that are up to 2 dm high. The strap-shaped leaves have entire to broadly-toothed margins and short petioles and are 2-6 cm long, becoming smaller up the stem. Foliage is sparsely covered with grayish, appressed hairs. The flowers are borne on their long, stalk-like ovary in the axils of the crowded upper leaves. The flowers have 4 partly united, reflexed sepals that are 1-2 cm long. The 4 white petals become pink with age, are 15-30 mm long, and are wedge-shaped with broad tips. There are 8 stamens and a long style with an x-shaped stigma. Each flower surmounts a 15-35 mm long ovary that matures into a many-seeded capsule.
Lesica (2012) recognizes two subspecies for Montana: subsp. pallida and subsp. trichocalyx (Nutt.) Munz & W.M. Klein.
Phenology
Flowering occurs in July-early August.
Diagnostic Characteristics
Our only subspecies of Oenothera pallida in the state. There are two other species of white-flowered, leafy-stemmed evening-primroses in Montana. Oenothera albicaulis is a more delicate, taprooted annual. Oenothera nuttallii is very similar, but the inflorescence is glandular.
Species Range
Montana Range
Range Descriptions
Native
Range Comments
BC south to AZ and NM (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Observations in Montana Natural Heritage Program Database
Number of Observations: 16
(Click on the following maps and charts to see full sized version)
Relative Density
Recency
(Observations spanning multiple months or years are excluded from time charts)
Habitat
This plant is restricted to early successional sandy habitats. It grows on the crests and slopes of blowout areas in the Centennial Valley sandhills. Common associated species include Agropyron dasystachyum, Stipa comata, Cryptantha fendleri, Eriogonum ovalifolium, Psoralea tenuiflora, Phacelia hastata, Astragalus ceramicus, and Allium textile.
National Vegetation Classification System Groups Associated with this Species
Grassland
Lowland - Prairie Grassland
Ecology
POLLINATORS The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap:
Bombus pensylvanicus and
Bombus impatiens (Colla and Dumesh 2010).
Management
Pale evening-primrose grows in the sand dune region of the Centennial Valley where there is light to moderate grazing (Culver 1993). In 1987, the populations were reported to be thriving, however in 1993, only a few small populations were observed. Like other rare plants of the sandhills, this species requires the open sand of early successional areas, and declines when plant succession leads to later successional stages in which vegetation colonizes areas of formerly open sand (Lesica and Cooper 1998). Historically, the diversity of sandhills plant communities was influenced by a fire cycle of 20-30 years and pocket gopher (Thomomys talpoides) activity which maintained a significant proportion of early successional habitat. Pale evening-primrose would benefit from restoration of the fire regime and moderate grazing, at least in years following burns. Severe destabilization of the dunes, e.g. from off-road vehicles, could damage its habitat.
Stewardship Responsibility
Threats or Limiting Factors
STATE THREAT SCORE REASON
Reported threats to Montana's populations of Pale Evening-primrose (Oenothera pallida ssp. pallida) are currently assigned as unknown. Potential threats due to management actions that exclude disturbance in appropriate habitat need to be substantiated before a threat rank can be assigned (MTNHP Threat Assessment 2021).
References
- Literature Cited AboveLegend:
View Online Publication
Colla, S.R. and S. Dumesh. 2010. The bumble bees of southern Ontario: notes on natural history and distribution. Journal of the Entomological Society of Ontario 141:39-68.- Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
- MTNHP Threat Assessment. 2021. State Threat Score Assignment and Assessment of Reported Threats from 2006 to 2021 for State-listed Vascular Plants. Botany Program, Montana Natural Heritage Program, Helena, Montana.
- Additional ReferencesLegend: View Online Publication
Do you know of a citation we're missing?- Culver, D.R. 1994. Floristic analysis of the Centennial Region, Montana. M.Sc. Thesis. Montana State University, Bozeman. 199 pp.
- Lesica, P., M.T. Lavin, and P.F. Stickney. 2022. Manual of Montana Vascular Plants, Second Edition. Fort Worth, TX: BRIT Press. viii + 779 p.
- Web Search Engines for Articles on "Pale Evening-primrose"
