San Benito Evening-primrose

Camissonia benitensis

Description

San Benito evening-primrose, Camissonia benitensis, is a low-growing, annual herb with oblong, alternate, hairy leaves, hairy stems, and bright yellow flowers. San Benito evening-primrose resembles C. contorta, a more common species, but differs in chromosome number, the most reliable method of differentiating species.

Habitat

San Benito evening-primrose is apparently restricted to serpentine soils of alluvial terraces, or in relatively barren deposits of alluvial gravel, along valleys of streams that feed into the San Benito River. The species' dependence upon on riparian influence seems more related to the soil conditions than to the water itself. This primrose is not found in damp areas along streams but in dry soils adjacent to streams. It seems to prefer relatively flat terraces with slight to moderate slope. It grows best in open areas with full sun exposure throughout the day.

The climate in the San Benito Mountains/Clear Creek area is hot and dry in summer and cool and wet in winter. Temperatures can be quite extreme, falling below freezing in winter to exceeding 100°F (37.8°C) in summer. Habitat elevation ranges from 2,500-4,600 ft (760-1,340 m).

Distribution

The plant was discovered in 1960 in the Clear Creek Reservation Area and is probably endemic to the San Benito River Valley in central California

As of 1985, San Benito evening-primrose grew in nine colonies of 10-150 plants each, totaling less than 1,000 plants, along Clear Creek and San Carlos Creek between Hernandez and New Idria. All sites are in San Benito County. Eight colonies are located on Bureau of Land Management (BLM) lands; one site is privately owned.

Threats

The population on private land, one of the largest, is near the west entrance to Clear Creek Canyon. Gravel mining has destroyed or severely damaged many plants and threatens to eliminate this population altogether if an agreement cannot be reached with the land owner—the mining company.

Conservation and Recovery

The BLM has fenced plants on public land to protect them from the incursions of off-road vehicles, a common recreational activity in the area. Plants inside fences are apparently increasing in number, although slowly. Plants outside continue to decline because of direct destruction by vehicles or erosion triggered by vehicle ruts. Federal land at Clear Creek Canyon has been designated a recreation area for off-road vehicles, but the BLM has developed a plan to protect plants there. The plan recommends fencing sites. Camping near some of the plant colonies increases opportunities for disturbance or casual collecting, making management difficult.

Little is known about the environmental requirements of this species but it appears to have only a moderate reproductive capacity even under favorable conditions. Even with full protection, the plant may not significantly expand its range for many years.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

References

Bureau of Land Management. 1986. "Clear Creek Management Plan and Decision Record." BLM, Bakersfield District, Hollister Resources Area. 81 pp.

Griffin, J. R. 1978. "Survey of Rare and Endangered Plants of the Clear Creek Recreation Area." Report CA-040-PH8-078. Folsom District, BLM.

Kiguchi, L. M. 1983. "Sensitive Plant Survey: Clear Creek Recreation Area and San Benito Mountain Natural Area." Report. Hollister Resource Area, BLM.

Raven, P. H. 1969. "A Revision of the Genus Camissonia (Onagraceae)." Contributions to the U.S. National Herbarium 37:332-333.

Florence, S. and L. M. Kiguchi. 1986. "Sensitive Plant Survey: Clear Creek Recreational Area, San Benito Mountain National Area." Bureau of Land Management, Hollister Resources Area.