Endangered Species Recovery Program
San Joaquin woolly-threads is an annual herb and the sole species in the genus Lembertia. The common name "woolly-threads" is derived from the many long (up to 45 cm; 18 inches) trailing stems covered with tangled hairs. However, the growth habit varies;San Joaquin woolly-threads plants also can be tiny (<7 cm; <3 inches) and erect with a single stem. The tiny, yellow flowers are clustered at the tips of the stems and branches. Each flower head is approximately 6 mm (0.25 inches) 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.
The phenology of San Joaquin woolly-threads varies with weather and site conditions. In years of below-average precipitation, few seeds of this species germinate, and those that do typically produce tiny plants. 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 those farther south. Each plant may have from 1 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 after 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.
Insect pollinators are not required for seed-set of this species. However, animals may be important to this plant species in other ways. For example, giant kangaroo rat (Dipodomys ingens) activity contributes to greater plant size and flower head production in San Joaquin woolly-threads where the two species co-occur, probably by increasing available soil nutrients and reducing competition from other plants. The microhabitat offered by giant kangaroo rat precincts (burrow systems) 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.
San Joaquin woolly-threads occurs in Non-native Grassland, Valley Saltbush Scrub, Interior Coast Range Saltbush Scrub, and Upper Sonoran Subshrub Scrub. This species typically occupies microhabitats with less than 10% shrub cover, although herbaceous cover may be either sparse or dense. Plant species that often occur with San Joaquin woolly-threads include red brome (Bromus madritensis ssp. rubens), red-stemmed filaree (Erodium cicutarium), goldfields (Lasthenia spp.), Arabian grass (Schismus spp.), and mouse-tail fescue (Vulpia myuros). Hoover's woolly-star (Eriastrum hooveri) often occurs in populations of San Joaquin woolly-threads, although the reverse is not true.
This species occurs on sandy,sandy loam, or silty soils with neutral to subalkaline pH that were deposited in geologic times by flowing water. Occurrences have been reported at elevations ranging from approximately 60 to 800 m (197 to 2,625 ft).
Historically, San Joaquin woolly-threads occurred primarily in the San Joaquin Valley, with a few occurrences in the hills to the west and in the Cuyama Valley of San Luis Obispo and Santa Barbara counties. Many new occurrences of San Joaquin woolly-threads have been discovered since 1986, primarily in the hills and plateaus west of the San Joaquin Valley. These constitute four metapopulations (scattered groups of plants that may function as a single population due to occasional interbreeding) and several small, isolated populations. The largest extant metapopulation occurs on the Carrizo Plain Natural Area in San Luis Obispo County. Much smaller metapopulations are found in Kern County near Lost Hills, in the Kettleman Hills of Fresno and Kings counties, and in the Jacalitos Hills of Fresno County. The isolated occurrences are known from the Panoche Hills in Fresno and San Benito counties, the Bakersfield vicinity in Kern County, and the Cuyama Valley.
Habitat loss was responsible for the decline of San Joaquin woolly-threads. The majority of the occurrences in the San Joaquin and Cuyama valleys were extirpated by intensive agriculture. In addition, several sites in and around Bakersfield were eliminated by urban and intensive oilfield development. Current threats to San Joaquin woolly-threads include commercial and agricultural development, increased intensity of land use in oilfields or pastures, and competition from introduced plants.
Order ASTERALES, Family ASTERACEAE, Genus Lembertia, Species congdonii
California Natural Diversity Database, Sacramento; Johnson, D.E. 1993. Lembertia. P. 303, in The Jepson manual: higher plants of California (J.C. Hickman, ed.). Univ. California Press, Berkeley, 1400 pp; Skinner, M.W., and B.M. Pavlik, eds. 1994. Inventory of rare and endangered vascular plants of California. Fifth edition. Spec. Publ. No. 1, California Native Plant Society, Sacramento, 338 pp.; Taylor, D.W. 1989. Status survey of San Joaquin woolly-threads (Lembertia congdonii). U.S. Fish and Wildlife Service, Sacramento, CA, Unpubl. Rep., 27 pp.
2-45 cm (3-18 inches)
Flower head length:
6 mm (0.25 inches)
San Joaquin woolly-threads differs from the related snowy eatonella (Eatonella nivea) in the shape of the florets and achenes and in geographical range.
N. L. Brown and E. A. Cypher