Endangered Species Recovery Program

13. Oil Neststraw (Stylocline citroleum)

• Taxonomy
• Description
• Historical Distribution
• Current Distribution
• Life History and Habitat
• Reasons for Decline and Threats to Survival
• Conservation Efforts
• Conservation Strategy

Taxonomy.-- Oil neststraw was recently recognized as a distinct species, Stylocline citroleum (Morefield 1992), even though herbarium specimens were collected as early as 1883. Munz collected the type specimen in 1935 from flats near Taft, in Kern County (Morefield 1992). Oil neststraw is believed to have originated as a hybrid of two common species, everlasting neststraw (Stylocline gnaphaloides) and California filago (Filago californica). However, oil neststraw satisfies the definition of a species because it is capable of reproducing itself without further crossing of the parental species (Morefield 1992). Oil neststraw is a member of the aster family.

Description.-- Oil neststraw is inconspicuous because it grows low to the ground and does not have showy flowers. It has trailing, woolly stems less than 13 centimeters (5 inches) long and small, woolly leaves. The round flower heads are 5 millimeters (0.2 inch) or less in diameter. Each flower head contains many individual florets, which consist of reproductive parts and papery scales covered with woolly hairs. The fruits are tiny, brown achenes. Oil neststraw is difficult to distinguish from closely related species because the identifying characters are microscopic (Morefield 1992, 1993).

Historical Distribution.-- Five populations of oil neststraw were known historically, based on collections made from 1883 to 1935 (Figure 36). Four of the occurrences were in Kern County, in the vicinities of Bakersfield, McKittrick, and Taft (two sites, including the type locality). The fifth collection was made in San Diego County.

Current Distribution.-- Oil neststraw is known currently from Elk Hills and the nearby Coles Levee Ecosystem Preserve in western Kern County (Figure 36) (Enterprise Advisory Services, Inc. 1997, 1998, QUAD 1997, Jay Hinshaw pers. comm.). The status of other western Kern County occurrences is unknown; although natural land remains at most sites, the location descriptions are vague. The east Bakersfield and San Diego occurrenes are less likely to remain due to rapid development in those areas.

Figure 36. Distribution of oil neststraw (Stylocline citroleum).

Life History and Habitat.-- Oil neststraw, an annual, flowers in April and reproduces strictly by self-pollination. The extant occurrences and several of the historical localities are in petroleum-producing areas, giving rise to both the common and scientific names. This species grows on flats and on slopes. One of the Elk Hills populations of oil neststraw occurs on the bank of a wash in a very sparsely vegetated area that has well-developed cryptogamic crust. The few plant species associated with oil neststraw at that site are natives such as everlasting neststraw, California filago, Hoovers woolly-star, and many-flowered eriastrum. Plant species that occur with oil neststraw in the other Elk Hills sites are red brome, common saltbush, and white burrobush (Hymenoclea salsola). All the extant occurrences are in the Valley Saltbush Scrub plant community in undeveloped areas. Oil neststraw has been found at elevations of 60 to 320 meters (200 to 1,050 feet) on both sandy and clay soils (Morefield 1992, EG&G Energy Measurements unpublished data, D. Taylor pers. comm.).

Reasons for Decline and Threats to Survival.-- Urban development has almost certainly eliminated the historical populations of oil neststraw in the vicinities of San Diego and Bakersfield, and possibly the one near Taft (Skinner and Pavlik 1994). Petroleum production is the primary use in the other areas where oil neststraw occurred historically, but actual population losses to oilfield activities have not been documented. The known populations on Elk Hills are not in an area with high potential for oil extraction (B.L. Cypher pers. comm.). However, any surface-disturbing activities would be detrimental to oil neststraw (J. Morefield pers. comm.).

Conservation Efforts.-- Most conservation efforts to date for oil neststraw have been accomplished by U.S. Department of Energy and their contractors in the Endangered Species and Cultural Resources Program at Elk Hills. Floristic surveys funded by the U.S. Department of Energy (1995-1997) and Occidental Petroleum (1998) revealed the presence of numerous new occurrences of oil neststraw scattered throughout Elk Hills (Enterprise Advisory Services, Inc. 1997, 1998, J. Hinshaw pers. comm.). Oil neststraw also was discovered at the adjacent Coles Levee Ecosystem Preserve during surveys funded by ARCO Western Energy (QUAD 1997). Morefield verified the identity of Elk Hills specimens collected through 1997. J. Hinshaw has developed a field key to oil neststraw and related species to facilitate identification and to permit mapping of occurrences, and he has conducted workshops to train local biologists in recognizing the species (J. Hinshaw pers. comm.). U.S. Department of Energy entered into a voluntary agreement with USFWS to protect four of the known populations on Elk Hills while the area was in government ownership. One or more of these occurrences are likely to be included in the conservation area that Occidental Petroleum will set aside in 1998 (B.L. Cypher pers. comm.).

Conservation Strategy.-- The strategy for oil neststraw is similar to that for other species of concern: to protect at least five distinct populations representing the full geographic range of the species in the San Joaquin Valley. The known occurrences at Elk Hills represent a single metapopulation and collectively constitute one of the five required populations. Protected areas should be natural land in blocks of at least 65 hectares (160 acres) and should contain a minimum of 1,000 individuals to reduce the likelihood of extinction from intrinsic or random processes.

Several tasks are necessary to ensure long-term conservation of oil neststraw. First, the local populations at Elk Hills must be protected from disturbance (deliberate or accidental) for the foreseeable future. Occidental Petroleum could accomplish this goal by including representative populations of oil neststraw in their Elk Hills conservation area. Next, intensive surveys should be undertaken in suitable habitats throughout the southern San Joaquin Valley. The species has been overlooked in he past because it is so small, because it grows intermixed with superficially similar plants, and because it was not recognized as a species until 1992. However, the availability of keys based on both field and microscopic characters and Morefields willingness to identify questionable specimens should overcome most limitations to species identification. The nature and magnitude of threats should be determined for all populations that are discovered, and steps should be taken to prevent habitat loss or degradation. In addition, site factors should be characterized to provide clues to the species habitat requirements. Representative populations should be monitored annually to evaluate population trends. The status of oil neststraw should be reevaluated within 5 years of recovery plan approval.