Eureka Valley Evening-primrose

Oenothera avita ssp. eurekensis

Description

Eureka Valley evening-primrose, Oenothera avita ssp. eurekensis, is a perennial herb that forms a rosette, 4-5 in (10-12 cm) across. The stems rise from deep-seated, fleshy, underground, creeping roots. The large, conspicuous flowers are white to pink with prominent yellow stamen. Stem and leaf growth begins in April and budding occurs through early July. The flowers open in the evening and close the following morning. Fruit is produced May through July, and seed dispersal occurs in June and July. After the seeds have set during the summer, all the leaves fall and new rosettes form at the tips of the old fruiting shoots. If the plant is buried by sand, it returns to the rosette stage.

Habitat

The Eureka Valley evening-primrose roots in the shallower sands bordering the dunes proper, often well away from the slopes. The lower dunes are stable with a gentle slope. Habitat elevation varies between 2,900 and 4,000 ft (900 and 1,200 m). Normally the valley floor is dry, but during times of heavy runoff it becomes a shallow, temporary lake. Summer temperatures are hot (often 104°F—40°C— or hotter); winter days usually rise above freezing. Most of the rainfall occurs November through March, supplemented by summer thunderstorms.

The flora of the Eureka Valley Dunes is unique and extremely valuable in terms of its scientific interest. The associated Eureka Valley dunegrass (Swallenia alexandrae ) has also been federally listed as Endangered.

Distribution

This species is endemic to Eureka Valley, situated in eastern California in Inyo County, 25 mi (40 km) east of Big Pine. The valley is bounded by the Inyo Mountains to the north and west, the Saline Range to the south, and the Last Chance Mountains to the east.

The largest evening-primrose population is found in the valley east of the main ridge of the Eureka Dunes. Elsewhere, plants are more scattered but still fairly numerous. Marble Canyon at the southwest corner of Eureka Valley supports a population, as does Saline Spur Dunes, west of the Eureka Dunes.

Threats

The Bureau of Land Management (BLM) administers the entire Eureka Valley, except for a few parcels that are state-owned. The area has never been surveyed into sections and townships, and agriculture has never penetrated to the southern part of the valley. The Death Valley National Monument begins a short distance to the southeast.

For a long time Eureka Valley was fairly inaccessible, which protected its delicate ecology from disturbance, but during the 1960s, off-road vehicle enthusiasts began to use its steep slopes for recreation. The resulting traffic caused immense damage to the habitat. When the Eureka Dunes were designated as a Special Design Area in 1976, the area was closed to off-road vehicles, and the dune ecology has recovered rapidly.

Conservation and Recovery

For the full recovery of the evening-primrose, transplanting and seeding to supplement natural reproduction will probably be unnecessary. Current road closures and camping prohibitions should be sufficient if enforced. A management plan produced by the BLM has recommended that camping and picnic sites be located away from the sensitive dune borders and slopes, so that visitors may still enjoy the beauty without damaging the habitat.

Contact

Regional Office of Endangered Species
U. S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

References

Bagley, M. 1986. "Baseline Data for a Sensitive Plant Monitoring Study on the Eureka Valley Dunes, Inyo County, California." Bureau of Land Management, Riverside, CA. BLM Contract number CA-065-R04-61. 104 pp.

DeDecker, M. 1979. "Can BLM Protect the Dunes?" Fremontia 7:6-8.

Munz, P. A. 1974. A Flora of Southern California. University of California Press, Los Angeles.

Roll, L. A. 1979. "Can BLM Protect the Dunes?—A Reply." Fremontia 7:8.

U.S. Fish and Wildlife Service. 1982. "The Eureka Valley Dunes Recovery Plan." U.S. Fish and Wildlife Service, Portand.

Wilshire, H. G. and J. K. Nakata. 1976. "Off-Road Vehicle Effects on California's Mojave Desert." California Geology 29:123-132.