|(Munz) Raven, Dietrich & Stubbe|
|Edward Guerrant, Ph.D.|
The following Participating Institutions are custodians for this species in the CPC National Collection:
Rae Selling Berry Seed Bank & Plant Conservation Programs
The conservation of Oenothera wolfii is fully sponsored.
Edward Guerrant, Ph.D. contributed to this Plant Profile.
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
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.
|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).
Conservation, Ecology & Research
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.
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.).
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).
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).
Meinke, R.J. 1982. Threatened and Endangered Vascular Plants of Oregon: An Illustrated Guide. Portland, Oregon: U.S. Fish & Wildlife Service, Region 1. 326p.
Tillford, G.L. 1997. Edible and Medicinal Plants of the West. Missoula, Montana: Mountain Press Publishing Company. 239p.