San Joaquin Woolly-threads

Lembertia congdonii

Description

The common name "woolly-threads" for Lembertia congdonii is derived from the many long (up to 18 in [46 cm]), trailing white stems covered with tangled hairs. San Joaquin woolly-threads plants, however, can also be tiny—less than 3 in (7.5 cm)—and erect with a single stem. The tiny, yellow flower heads are clustered at the tips of the stems and branches. Each flower head is approximately 0.25 in (6 mm) long and contains two types of florets (the tiny flowers characteristic of the aster family); the four to seven outer florets differ in shape from the numerous inner florets. The two types of florets produce achenes (tiny, one-seeded fruits) that also differ in shape. San Joaquin woolly-threads—which is also known as Congdon's eatonella and which has also been classified as Eatonella congdonii —differs from snowy eatonella (E. nivea ) in the shape of the florets and achenes.

Seed germination may begin as early as November but usually occurs in December and January. San Joaquin woolly-threads typically flowers between late February and early April, but flowering may continue into early May if conditions are optimal. Populations in the northern part of the range flower earlier than does the Carrizo Plain metapopulation. Each plant may have from one to more than 400 flower heads. Seed production depends on plant size and the number of flower heads; in 1993, achene production ranged from 10 to 2,500 seeds per individual. The seeds are shed immediately upon maturity, and all trace of the plants disappears rapidly after their death in April or May. Seed dispersal agents are unknown, but possible candidates include wind, water, and animals. Seed-dormancy mechanisms apparently allow the formation of a substantial seed bank in the soil.

Although insect pollinators are not required for seed set in San Joaquin woolly-threads, animals may be important to this plant species in other ways. On the Carrizo Plain Natural Area, giant kangaroo rat activity contributes to greater plant size and flower head production in San Joaquin woolly-threads, probably by increasing available soil nutrients and reducing competition from other plants. The microhabitat offered by giant kangaroo rat precincts also contributes to earlier seed germination and maturation of San Joaquin woolly-threads, possibly because precinct surfaces are warmer than the surrounding area during the winter months.

Habitat

San Joaquin woolly-threads occurs in non-native grassland, Valley saltbush scrub, Interior Coast Range saltbush scrub, and Upper Sonoran sub-shrub scrub. This species typically occupies micro-habitats with less than 10% shrub cover, although herbaceous cover may be either sparse or dense, and cryptogamic crust may or may not be present. Plant species that often occur with San Joaquin woolly-threads include red brome, red-stemmed filaree, goldfields, Arabian grass, and mouse-tail rescue. Hoover's woolly-star often occurs in populations of San Joaquin woolly-threads.

San Joaquin woolly-threads occurs on neutral to subalkaline soils that were deposited in geologic times by flowing water. On the San Joaquin Valley floor, this species typically is found on sandy or sandy loam soils, particularly those of the Kimberlina series, whereas on the Carrizo Plain it occurs on silty soils. San Joaquin woolly-threads frequently occurs on sand dunes and sandy ridges as well as along the high-water line of washes and on adjacent terraces. Occurrences have been reported at elevations of approximately 200-850 ft (60-260 m) on the San Joaquin Valley floor and surrounding hills, and 2,000-2,600 ft (600-800 m) in San Luis Obispo and Santa Barbara Counties.

Distribution

San Joaquin woolly-threads historically occurred on the valley floor. Four known populations were from the Cuyama Valley and the remainder from the hills of the San Joaquin Valley. Many new occurrences have been discovered since 1986, primarily in the hills and plateaus west of San Joaquin Valley. The largest, on the Carrizo Plain Natural Area, occupies habitat of more than 2,800 acres (1,130 hectares) in years of high rainfall. Much smaller populations occur near Lost Hills and Jacalitos Hills.

Threats

Habitat loss was responsible for the decline of San Joaquin woolly-threads on the floors of the San Joaquin and Cuyama Valleys, where the majority of the occurrences were eliminated by intensive agriculture. In addition, several sites in and around Bakersfield were eliminated by urban development, and two others between Lokern and Lost Hills apparently were destroyed as a result of intensive oil field development. The Lost Hills metapopulation is on private land in an area of high value for commercial development and agriculture. Several occurrences in the Kettleman Hills, the Jacalitos Hills, and west of Bakersfield are in low-density oil fields; the plants do not seem to be threatened by the current level of activity but could be destroyed by more intensive use of the areas. Preliminary studies suggested that both competition from exotic plants and spring grazing reduced survival rates, but not flower production. Trampling also reduces survival in areas where livestock congregate, such as around water troughs.

Conservation and Recovery

The priority for ensuring the survival of San Joaquin woolly-threads is to protect existing habitat and monitoring populations. Many of the occurrences of San Joaquin woolly-threads are on lands administered by the U. S. Bureau of Land Management. Within these areas, fences have been constructed around populations that show evidence of trampling by livestock. The California Department of Fish and Game has funded research on the reproductive biology and ecology of the species, and other state agencies have sponsored surveys. A 300-acre (120-hectare) area west of Bakersfield is targeted to become a preserve.

Contacts

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

U. S. Fish and Wildlife Service
Sacramento Fish and Wildlife Office
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
Telephone: (916) 414-6600
Fax: (916) 460-4619

References

Heady, H. F. 1977. "Valley Grassland." In Terrestrial Vegetation of California, edited by M. G. Barbour and J. Major. Wiley, New York.

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

Taylor, D. W. 1987. "Status Survey of San Joaquin Woolly-threads (Lembertia congdonii )." U. S. Fish and Wildlife Service, Sacramento.

Wester, L. 1981. "Composition of Native Grasslands in the San Joaquin Valley, California." Madroño 28: 231-241.