Hoover's Woolly-star

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Hoover's Woolly-star

Eriastrum hooveri

ListedJuly 19, 1990
FamilyPolemoniaceae (Phlox)
DescriptionAnnual with fuzzy, wiry stems and small, white flowers.
HabitatValley and foothill scrub.
ThreatsOil and gas development; conversion to cropland; urbanization; livestock grazing.


The wiry stems of Hoover's woolly-star (Eriastrum hooveri ) may or may not branch and vary in height from 0.4-8 in (1-20.3 cm) at flowering. The leaves are threadlike and may have two narrow lobes near the base. Hoover's woolly-star has tiny, white to pale blue flowers that are nearly hidden in tufts of woolly hair. The stamens (male reproductive parts) are shorter than the corolla.

Many-flowered eriastrum (E. pluriflorum ) frequently occurs with Hoover's woolly-star; it has dark blue flowers that are 0.6 in (1.5 cm) or greater in length, stamens that protrude from the corolla, and leaves with up to 10 lobes. Eriastrum species that occur within the same range are distinguished from Hoover's woolly-star by flower color and stamen length.

Hoover' s woolly-star is an annual, but the seeds germinate later in the growing season than do those of many of the associated annual plants. Seedlings may emerge from January or February until mid-April. The typical flowering period for Hoover's woolly-star extends from March into June. Pollination ecology has not been investigated. However, other members of the genus Eriastrum are pollinated by native bees. The tiny seeds are probably dispersed by wind or by tumbling of dead stems. Unlike many other annuals, dead stems of Hoover's woolly-star may persist until the next growing season.

Within metapopulations, Hoover's woolly-star typically occurs as scattered groups of plants, with each group occupying an area of less than 1 acre (0.4 hectare). Densities of Hoover's woolly-star fluctuate from year to year and are highest in years of above-average precipitation. At Elk Hills, densities in natural colonies were five to 15 times greater in 1993, a year of above-average rainfall, than in 1991, which was a year of average rainfall.


Hoover's woolly-star seems to be much more adaptable than other endemic plants of the San Joaquin Valley. Optimal habitats for the species are characterized by stabilized silty to sandy soils, a low cover of competing herbaceous vegetation, and the presence of cryptogamic crust (a layer of moss, lichen, and algae). However, this species also has been found on loamy soils, in areas of dense vegetation, and in areas lacking cryptogamic crust. Hoover's woolly-star may reinvade disturbed soil surfaces such as well pads and dirt roads within a year after the disturbance ceases if seed sources remain in the vicinity. In fact, this species may benefit from light to moderate soil disturbance in areas that are densely vegetated by exotic plants.

Populations of Hoover's woolly-star occur in alkali sinks, washes, on both north-and south-facing slopes, and on ridgetops. This species occurs in a wide variety of plant communities. Most are characterized by shrubs such as common saltbush, seep-weed, and matchweed, but shrub cover in occupied habitats typically is less than 20%. Herbaceous plant species frequently found in association with Hoover's woolly-star include red brome, goldfields, many-flowered eriastrum, and red-stemmed filaree. Populations of Hoover's woolly-star have been reported at elevations ranging from 165-3,000 ft (50-914 m).


Prior to 1986, Hoover's woolly-star was known from 19 sites in four counties, based on herbarium collections and written observations. The majority of the occurrences were on the San Joaquin and Cuyama Valley floors, and the others were from the low mountains at the west side of the San Joaquin Valley.

Hoover's woolly-star since has been discovered in Kings and San Benito counties and at numerous additional sites in the four original counties, particularly in foothill areas. Most of the occurrences are concentrated in four metapopulations. Small, isolated populations occur in scattered areas in Fresno, Kern, San Benito, and Tulare counties.


Valley-floor populations of Hoover's woolly-star have been destroyed primarily by farming operations and secondarily by urban development. Some populations are threatened by commercial development, others by agricultural conversion. Floodingas a result of high precipitation, groundwater recharge programs, agricultural wastewater diversion, or waterfowl managementcould destroy populations in low-lying areas. Dense growth of associated vegetation (such as in areas where exotic grasses dominate or where fire has been suppressed) may create unsuitable conditions for growth of Hoover's woolly-star. Hoover's woolly-star remains primarily in hilly areas, many of which are oil fields; petroleum production does not pose a threat in most cases but could be detrimental if large areas of occupied habitat were disturbed. The acquisition of Elk Hills by Occidental Petroleum may lead to greater surface disturbance if rates of exploration and production are increased.

Conservation and Recovery

Occidental Petroleum, the owner of the Elk Hills oilfield, plans to set aside a conservation area containing Hoover's woolly-star, among other rare species. In addition, the U. S. Department of Energy has sponsored several research projects on the ecology of Hoover's woolly-star, its response to oilfield activity, and the conditions under which it will re-colonize disturbed areas. Hoover's woolly-star also has benefited from the acquisition of conservation lands for listed animals. In 1990 Mobil Oil Corporation constructed enclosures around Hoover's woolly-star on their lands in Lost Hills.

Recovery of Hoover's woolly-star can be accomplished using public lands and other areas already dedicated for conservation. As with the other listed plants, the goal is to protect populations throughout the species' range populations that represent a variety of topographic positions and community types. Considering that habitat conversion is ongoing in valley-floor areas and that oil production could increase on public lands, the continued existence of populations cannot be assumed unless a specific commitment is made to protect them from incompatible uses. Some amount of unoccupied suitable habitat is important to allow population fluctuations among years, and a buffer zone is important to minimize external influences.


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

Sacramento Field Office
Federal Building
2800 Cottage Way
Sacramento, California 95825-1846
Telephone: (916) 414-6446
Fax: (916) 414-6486


Hoover, R. F. 1970. The Vascular Plants of San Luis Obispo County, California. University of California Press, Berkeley.

Taylor, D. W., and W. B. Davilla. 1986. "Status Survey of Three Plants Endemic to the San Joaquin Valley." U. S. Fish and Wildlife Service, Sacramento.