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Recovery Plan for Upland Species of the San Joaquin Valley, California
Contents . Introduction . Species accounts . Recovery . Stepdown . Implementation . References . Appendix

4. Vaseks Clarkia (C. tembloriensis ssp. calientensis)

Taxonomy.-- Vaseks clarkia, a member of the evening-primrose family (Onagraceae), was described originally as a full species, Clarkia calientensis (Vasek 1977). The type locality of Vaseks clarkia is ". . . along Caliente Road, 10 kilometers E of the junction with the Bakersfield-Tehachapi highway" (Vasek 1977, p. 252). Based on its morphological similarity to the more common Temblor clarkia (Clarkia tembloriensis), Holsinger (1985) proposed the name C. tembloriensis ssp. calientensis, which is in current use (H. Lewis 1993). However, biosystematic studies in progress suggest that Vaseks clarkia is a unique taxon that originated independently of Temblor clarkia in recent times (T. Holtsford pers. comm.).

Description.-- Vaseks clarkia can grow up to 80 centimeters (30 inches) tall and has alternate, grayish-green, lance-shaped leaves. The flowers have four lavender-pink petals with narrow bases and diamond-shaped tips. The styles (part of the female reproductive system) are approximately the same length as the stamens. Vaseks clarkia has broader petals, shorter styles, narrower fruits, and larger seeds than Temblor clarkia, and both differ from gunsight clarkia (C. unguiculata) in that they lack long hairs on the flower parts (Holsinger 1985, H. Lewis 1993).

Historical Distribution.-- This taxon is endemic to the Caliente Hills of Kern County, which are southeast of Bakersfield (Skinner and Pavlik 1994). The historical distribution consisted of only the type locality, where the taxon was first collected in 1967 (Vasek 1977).

Current Distribution.-- Plants have not been observed at the type locality since 1982, despite repeated searches. However, two other occurrences were discovered west of the type locality in 1982 (Figure 21); they represent a single metapopulation (CDFG 1995, T. Holtsford pers. comm.).

Figure 21
Figure 21. Distribution of Vasek's clarkia (C. tembloriensis ssp. ssp. calientensis).

Life History and Habitat.-- Vaseks clarkia is an annual, flowers in April (Skinner and Pavlik 1994), and is self-pollinating. The timing of seed germination in the wild is not known, but in greenhouse tests, plants that were started from seed in January had a higher reproductive output than those that were started in November (Vasek 1977). The closely-related Springville clarkia (Clarkia springvillensis) forms a persistent seed bank, and this taxon may as well (T. Holtsford pers. comm.). Vaseks clarkia grows in steep-sided canyons on grassy north- and west-facing slopes at elevations of 275 to 335 meters (900 to 1,100 feet). Associated species include bladderpod, farewell-to-spring (Clarkia cylindrica), and gunsight clarkia (CDFG 1995). The extant metapopulation comprises several thousand individuals in favorable years but has extremely low genetic variability (T. Holtsford pers. comm.).

Reasons for Decline.-- The reason for the disappearance of Vaseks clarkia from the type locality is unknown. The other two occurrences have not declined.

Threats to Survival.-- Vaseks clarkia is a very narrow endemic because of its extremely limited range, small population size, and lack of genetic variability. Thus, Vaseks clarkia is very vulnerable to extinction from random catastrophic events. All three of the reported occurrences were on private property, some of which is owned by the Tejon Ranch Company. Most of the occupied habitat is too steep to be developed or heavily grazed (T. Holtsford pers. comm.). Competition from exoticgrasses is believed to be the primary threat to this taxon (T. Holtsford pers. comm.).

Conservation Efforts.--Vasek and his colleagues have conducted taxonomic and genetic research, surveyed limited areas in the Caliente Hills, and monitored Vaseks clarkia since the species was first described. However, access to the sites has been restricted by the land owner in recent years (CDFG 1995, T. Holtsford pers. comm.). No other conservation measures have been instituted to date, but Kern County may provide incentives for conservation of the populations through the Valley Floor Habitat Conservation Plan (T. James pers. comm.).

Conservation Strategy.--Although Vaseks clarkia is a narrow endemic, at least five separate populations should be protected to increase the probability of long-term survival. 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. Conservation of Vaseks clarkia entails maintaining compatible uses at the known sites, controlling exotic grasses, surveying suitable habitats for additional populations, and banking seed as a safeguard against extinction. Conservation agreements with the private landowners are recommended, even though development is not expected in the area in the near future. Holtsford (pers. comm.) recommends continued light grazing to control grasses. Monitoring will be important to evaluate population trends; changes in site management may be necessary if declining population trends are observed. Surveys for Vaseks clarkia could be coordinated with those for California jewelflower and Bakersfield cactus, which occurred historically in the Caliente Hills, and where potential habitat still exists. Seed collections would not need to be large to be representative of the gene pool in the extant metapopulation but should be conducted according to Center for Plant Conservation (1991) recommendations. Introduction of the subspecies outside of the known range is not recommended, but planting of seeds in nearby suitable habitats within the historic range may be necessary to achieve the required number of populations if surveys prove unsuccessful. The status of Vaseks clarkia should be reevaluated within 5 years of recovery plan approval.

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