CPC National Collection Plant Profile

Oenothera wolfii

Tom Kaye

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CPC National Collection Plant Profile

Oenothera wolfii

Common Name: 
Wolf's evening-primrose
(Munz) Raven, Dietrich & Stubbe
Growth Habit: 
CPC Number: 


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 Fish & WildLife

Oenothera wolfiienlarge
Photographer: Tom Kaye

Oenothera wolfii is Not Sponsored
Primary custodian for this plant in the CPC National Collection of Endangered Plants is: 
Edward Guerrant, Ph.D. contributed to this Plant Profile.

Oenothera wolfii

Of all the many ways to be driven to extinction, Wolf's evening primrose is under assault from one of the most insidious and bizarre; its own offspring! We believe that children are a blessing. We believe that genetic diversity and the mixing of genomes is a good thing. In the botanical world, these assumptions aren't always true.
Oenothera wolfii grows along the coast of Oregon and northern California. It has been found growing in cracks in a parking lot, along the upper strand of the beach, on bluffs above the ocean, and along roadsides; all areas subject to a moderate amount of disturbance especially from sea spray and blowing sand. It exhibits many characteristics typical of an "opportunist" species such as high germination rates and low seedling survival. According to a local botanist, Oenothera wolfii "is as easy to grow as any I've seen, which makes one wonder why it is so rare" (Stansell 1989).

So, what makes this plant rare? Its peculiar habitat limits it to specific sites along the coast. It is found mostly on discontinuous patches of Cenozoic-era marine deposits, which are isolated from each other by other sedimentary and metamorphic rock. This may explain the disjunct distribution of the species. Within these sites, it requires well-drained soils with adequate moisture, minimal competition and protection from northwesterly exposure. The infrequency of sites that match these conditions may contribute to its rarity.

Rarity, in and of itself, is not necessarily of great conservation concern. What is of concern, however, are the multitude of threats to this species. This rare plant is, like so many other species, threatened by loss of habitat due to urban expansion and road paving, and from direct damage to plants by construction and herbicide spraying. Competition from non-native plants is also a problem. The threat from its own offspring is the most damaging and worrisome. Perhaps the most serious and most worrisome threat is from its own offspring.

The ornamental species Oenothera glazioviana originated in Europe, apparently as a stabilized hybrid between two North American species brought to Europe for ornamental purposes. It has been spreading around the globe, not only as a garden plant, but also as a weed. Oenothera glazioviana has become naturalized on every continent except Antarctica. Oenothera glazioviana is an out-breeder and is able to accept pollen from O. wolfii, thus producing viable hybrid offspring. Oenothera wolfii is an inbreeding species and apparently cannot accept pollen from other species. However, O. wolfii has been found to be receptive to pollen from the hybrids, and introgression, or the infiltration of one species' genes into another, is occurring. The genetic integrity of Wolf's evening primrose throughout much of the range in California is questionable (Imper 1997). Scientists are concerned that all O. wolfii genotypes will be diluted by the influence of O. glazioviana and this unique species will vanish from existence.

Why bother maintaining the genetic integrity of this species? As a part of a natural ecosystem, Oenothera wolfii plays an important ecological role. We may not fully understand the full impact of its value and its relationship to other species until it is gone. This species may also prove to be useful to humans, and if we allow it to become extinct, we may never know the benefits (see the ecology section for more).

Distribution & Occurrence

State Range
State Range of  Oenothera wolfii
  Oenothera wolfii can be found on sandy soil in grasslands, coastal strand, roadsides, and coastal bluffs, which are well drained but with adequate moisture. Sites are often in areas protected from northwesterly exposure, usually situated south of a headland or promontory or near the mouth of a river.

  Found in Del Norte and Humboldt counties in California and on the southern coast range in Oregon.

Number Left
  As of 1997: Approximately 16 sites (7 sites in Oregon, 9 California), scattered over 160 miles (260 km) of coastline between Cape Mendocino, CA and Port Orford, OR.

6 sites contained fewer than 50 individuals, 5 contained 100-1000, 4 contained 2000-3000, and one had more than 5,000 (Imper 1997).


Global Rank:  
Guide to Global Ranks
Federal Status:  
Guide to Federal Status
Recovery Plan:  

State/Area Protection
  State/Area Rank Status Date  
  California S1.1 7/1/2001  
  Oregon S1 LT 7/12/1995  

Conservation, Ecology & Research

Ecological Relationships
  Despite its tolerance to disturbances, tolerance for high salt concentrations in the soil, and high germination rates, (Imper 1987) Oenothera wolfii has a fairly restricted distribution. It requires protection from northwesterly exposure along the coast and so often occurs either at the mouth of a river or to the south of a major headland. If the plants occur on a bluff, it is always south of a small ridge (Imper 1988). Moisture throughout much of the year appears necessary to sustain young plants until the long taproot develops. This requirement for available moisture is often in conflict with the apparently low tolerance for competition (Imper 1997).

Oenothera wolfii is considered a facultative perennial. Under average conditions, O. wolfii is a typical biennial. It germinates in its first year and produces a small rosette. The following year it bolts, flowers, sets seed, and then dies. Under conditions of stress, a plant may wait several years before flowering. Rosettes begin bolting in April and flower in May or June. As the coastal climate is mild, flowering may continue into the winter or even last an entire year. Oenothera wolfii is self-pollinating (Imper 1997).

Oenothera wolfii hybridizes with O. glazioviana (a large flowered ornamental species). The hybrid appears to be more aggressive than either parent is; however, the hybrid does not seem to grow in the same soils as O. wolfii. The hybrid does well in gravelly, roadside soils, which may be imported, while O. wolfii prefers native, sandier soils (Imper 1987). The hybrids are also not as tolerant of salt and other climatic factors as O. wolfii.

Over half of the populations are threatened by hybridization. One isolated population in California and most of the Oregon populations are relatively unaffected by residential development and have little or no exposure to O. glazioviana. With the threat of hybridization, there is little preventative action that can be taken other than to protect isolated populations and prevent the introduction of O. glazioviana into those areas (Imper 1987).

In general members of the genus Oenothera have many culinary and medicinal uses. The roots, when young, can be cooked and eaten as a vegetable. The leaves and stems are mucilaginous and can be made into a tea for sore throats and raspy coughs. It also treats gastric irritations and when applied topically reduces swelling. Gamma-linolenic acid found in the seeds regulates fatty acid imbalances and metabolic functions of the liver. Clinical studies have demonstrated that Oenothera spp. can be used to treat vascular disease, asthma, arthritis and premenstrual syndrome (Tilford 1997). These uses have not been tested specifically on Oenothera wolfii. If we allow this species to be driven to extinction or "hybridized" out of existence, we may never know how beneficial it could have been. Although there may be many uses for this plant, it should not be wild collected because of its fragile state in the ecosystem.

  The greatest threat to this species is the displacement of natural populations by fertile plants resulting from hybridization with Oenothera glazioviana leading to the eventual genetic swamping of the O. wolfii genotype (Imper 1997).
Coastal development, road construction (Meinke 1982).
Herbicide applications (Meinke 1982).

Current Research Summary
  Germination studies comparing different temperature regimes. Alternating 59F/77F (15C/25C) resulted in the greatest germination percentages for 3 of the 10 seed lots tested (each lot from different parent plants) (Kaye 1999). For 7 of the 10 seed lots, the 15C/25C treatment was statistically indistinguishable from the 68F/86F (20C/30C) treatment. Constant 59F (15C) and constant 68F (20C) treatment showed much lower germination percentages (Kaye 1999).
Germination trials at the Berry Botanic Garden. Two different lots of seed from different parents were subjected either to 8 weeks of cold stratification or no cold stratification. That was followed by either constant 68F (20C) or alternating 50/68F (10/20C) temperatures. For the first batch (old seeds), All treatments had 60% germination except the no cold stratification treatment which had 100% germination. For the second batch (new seed), the cold stratified-50/68F treatment had 80% germination. Both the cold stratified 68F treatment and the straight 68F treatment had 60% germination. The straight 50/68F treatment had 40% germination (BBG File).
Informal germination studies/observations. High germination percentages with no treatment and no cold stratification. Highest germination rates in sandy potting mixture (~50%). Seeds germinated rapidly after sowing (Stansell 1989).
Researchers with the Oregon Department of Agriculture have developed effective cultivation protocols for O. wolfii in the greenhouse (Gisler, pers. comm.).
Ongoing research into determining the hybrid status of its extant populations (hybrids with introduced Oenothera glazioviana) (Gisler, pers. comm.)
Researchers at the Oregon Department of Agriculture are planning future work to cultivate and outplant this species to start new populations that are secure from the threat of hybridization (Gisler, pers. comm.).

Current Management Summary
  Mitigation project near Trinidad, Humboldt County, CA. Plants were transplanted from the area to be paved over and seeds collected that year were sown in suitable habitat. There was initial success, as the number of flowering individuals increased through 1993. The population declined from 1994-1995 and now seems to be sustained at a very low level (Imper 1997).
Approximately 300,000 seeds were spread in a variety of habitats along a County right-of-way in Northern California in order to establish a widespread population (Imper 1997).

Research Management Needs
  Suggested legal protection in California (Imper 1997).
Ban use of herbicide in habitat occupied by Oenothera wolfii (Imper 1997).
Limit roadside maintenance to periods after seed has matured in the summer and before re-growth in the spring (Imper 1997).
Public outreach project to limit the use of Oenothera glazioviana in the garden and encourage the use of native species (Imper 1997).
Establish new populations in areas isolated from the threat of Oenothera glazioviana (Imper 1997).

Ex Situ Needs
  Collect and store seed from across the species range. Attempt to get seed from "pure" stands of Oenothera wolfii.


Books (Single Authors)

Meinke, R.J. 1982. Threatened and Endangered Vascular Plants of Oregon: An Illustrated Guide. Portland, Oregon: U.S. Fish & Wildlife Service, Region 1. 326p.

Nakamura, Gary; Kierstead Nelson, J. 2001. Illustrated Field Guide to Selected Rare Plants of Northern California. University of California, Agriculture and Natural Resources. Publication 3395. 370p.

ONHP. 2001. Rare, Threatened and Endangered Plants and Animals of Oregon.

Tillford, G.L. 1997. Edible and Medicinal Plants of the West. Missoula, Montana: Mountain Press Publishing Company. 239p.

Books (Sections)

Imper, D.K. 1997. Ecology and Conservation of Wolf's Evening Primrose in Northwestern California. In: Kaye, T.N.; Liston, A.; Love, R. M.; Luoma, D.L.; Meinke, R.J.; Wilson, M.V., editors. Conservation and Management of Native Plants and Fungi. Native Plant Society of Oregon. Corvallis, Oregon. p 34-40.

Books (Edited Volumes)

James C. Hickman, Editor. 1993 The Jepson manual: Higher plants of California. Berkeley: University of California Press. 1400p.

Electronic Sources

(2000). CalFlora: on California plants for education, research and conservation. [web application]. Berkeley, California: The CalFlora Database [a non-profit organization]. http://www.calflora.org/.. Accessed: 2002.

CDFG. (2001). Special Vascular Plants, Bryophytes, and Lichens List. Biannual Publication, Mimeo. 141 pp. California Department of Fish and Game, Natural Diversity Database. Accessed: 2001.

CNDDB. (2000). Calfornia Natural Diversity Data Base (CNDDB). Version 2.1.2. California Natural Diversity Database. Accessed: California Department of Fish and Game, Sacramento.

ONHDB. (2000). Oregon Natural Heritage Program Database. Portland, Oregon.

Journal Articles

1979. (Original Publication). Systematic Bot. 4: 242-252.

Ellstrand, N.C.; Schierenbeck, K.A. 2000. Hybridization as a stimulus for the evolution of invasiveness in plants?. Proceedings Academy Natural Sciences Philadelphia. 97, 13: 70437050.

Fieldsend, A.F.; Morison, J.I.L. 2000. Climatic conditions during seed growth significantly influence oil content and quality in winter and spring evening primrose crops (Oenothera spp.). Industrial Crops and Products. 12: 137-147.

Gordon, K.H.J.; Crouse, E.J.; Bohnert, H.J.; Herrmann, R.G. 1982. Physical mapping of differences in chloroplast DNA of the 5 wild type pastomes in Oenothera subsection Euoenothera. Theoretical & Applied Genetics. 61, 4: 373-384.

Raven, P.H.; Dietrich, W.; Stubbe, W. 1979. An outline of the systematics Oenothera subsection Euoenothera Onagraceae. Systematic Botany. 4, 3: 242-252.

Stubbe, W.; Steiner, E. 1999. Inactivation of pollen and other effects of genome-plastome incompatibility in Oenothera. Plant Systematics and Evolution. 217, 3-4: 259-277.

USFWS. 1996. Notice of Reclassification of 96 Candidate Taxa. Federal Register. 61, 40: 7457-7463.

Wasmund, O.; Stubbe, W. 1986. Cytogenetic investigations on Oenothera-wolfii onagraceae. Plant Systematics & Evolution. 154, 1-2: 79-88.

Welty, J. 2001. Summer Intern Report: Native Plant Conservation Program. Bulletin of the Native Plant Society of Oregon. 34, 1: 1, 6-7.

Wolfson, R.; Higgins, K.G.; Sears, B.B. 1991. Evidence for replication slippage in the evolution of Oenothera chloroplast DNA. Molecular Biology and Evolution. 8: 709-720.

Personal Communications

Gisler, S. 2001. Personal Communication. Steve Gisler, Oregon Department of Agriculture, Plant Conservation Department, Corvallis, Oregon.

Imper, D.K. Dated September 4, 1988, 1988. Letter to Don Tuttle, Humboldt County Dept. of Public Works, Eureka, CA. On file at the Berry Botanic Garden.

Stansell, V. 1989. Letter to Kendra Mingo. On file at Berry Botanic Garden.


Imper, D.K. 1987. Overview: 1987 Field Survey, Oenothera wolfii in California. Unpublished report. p.3.

Kaye, T.N. 1999. Oenothera wolfii germination experiment. Unpublished data.

  This profile was updated on 7/8/2010
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