Hemizonia conjugens - Keck
Otay Tarweed
Synonym(s): Deinandra conjugens (D.D. Keck) B.G. Baldwin
Taxonomic Status: Accepted
Related ITIS Name(s): Deinandra conjugens (D.D. Keck) B.G. Baldw. (TSN 780273)
Unique Identifier: ELEMENT_GLOBAL.2.138990
Element Code: PDAST4R070
Informal Taxonomy: Plants, Vascular - Flowering Plants - Aster Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Asterales Asteraceae Hemizonia
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Concept Reference
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Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Hemizonia conjugens
Taxonomic Comments: USFWS lists this entity as federally threatened under the name of Deinandra conjugens. Kartesz uses the name Hemizonia conjugens in his 1999 Synthesis, but does not list any synonyms.
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 16Mar1999
Global Status Last Changed: 28Apr1989
Rounded Global Status: G1 - Critically Imperiled
Reasons: Endemic to southern San Diego County, California and adjacent Baja California, Mexico. Known from about twenty-two extant populations. At least 3 populations have been extirpated. Proposed development threatens most of the remaining populations; about 80% of the largest population (approximately 60% of the known annual individuals) is threatened by a single proposed housing project. Much of the potentially suitable habitat in the species' range has been cleared for agriculture; remaining habitat is often degraded by illegal dumping. Other threats are Border Patrol activities, including fencing and new facility construction, off-road vehicle activity, and airport expansion. The species is adapted to mild disturbances, such as grazing and road cuts.
Nation: United States
National Status: N1

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States California (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LT: Listed threatened (13Oct1998)
U.S. Fish & Wildlife Service Lead Region: R8 - California-Nevada

NatureServe Global Conservation Status Factors

Range Extent Comments: Restricted to a limited portion of southwestern San Diego County from Otay, south of San Diego, to the La Presa-Sweetwater Reservoir area ca. 8 mi ESE of San Diego, at 50-500 ft. Also collected 3 km southwest of La Presa, southeast of Tijuana, Baja, Mexico.

Number of Occurrences: 21 - 80
Number of Occurrences Comments: Twenty-two extant populations in California (Fish and Wildlife Service 1998).

Population Size Comments: Twelve of the twenty-two extant populations are considered major populations of more than 1000 individuals each. The largest population (Rancho San Miguel complex) supports about 200,000 individuals, more than 65% of all known plants. The five largest populations support about 94 % of all reported individuals (Fish and Wildlife Service 1994).

Overall Threat Impact Comments: Threatened by residential development and illegal dumping. Also threatened by intensive agriculture, off-road vehicle activity, Border Patrol activities, including facility construction, airport expansion, and the effects of habitat fragmentation (Fish and Wildlife Service 1998).

Intrinsic Vulnerability Comments: Mild distubances such as grazing and road cuts have probably prevented its complete extinction (CNPS Status Report, 1977).

Other NatureServe Conservation Status Information

Distribution
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Global Range: Restricted to a limited portion of southwestern San Diego County from Otay, south of San Diego, to the La Presa-Sweetwater Reservoir area ca. 8 mi ESE of San Diego, at 50-500 ft. Also collected 3 km southwest of La Presa, southeast of Tijuana, Baja, Mexico.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map

U.S. & Canada State/Province Distribution
United States CA

Range Map
No map available.

National Distribution Outside of U.S. & Canada: Mexico

U.S. Distribution by County Help
State County Name (FIPS Code)
CA San Diego (06073)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
18 San Diego (18070304)+, Cottonwood-Tijuana (18070305)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: An arromatic annual herb, 1-4 dm tall. Flower heads consist of 8-10 yellow ray flowers and 13-21 yellow disk flowers with black anthers. Blooms May-June.
Technical Description: "Stem 2-5 dm high, branching as in H. fasciculata; foliage and involucres soft-hirsute and sometimes hispidulose, especially the involucre bearing large flat and small capitate sessile or subsessile glands; heads solitary on short peduncles or subsessile in few-flowered glomerules; ray-flowers 8-10; disk flowers 13-21" (Munz, 1974).
Diagnostic Characteristics: Hemizonia conjugens can be characterized by ray flowers 8-13; phyllaries keeled; anthers black; plants annual herbs (Munz, 1974).
Duration: ANNUAL
Reproduction Comments: The dark seeds of tarweeds are used as food by many birds and also by rodents.
Terrestrial Habitat(s): Shrubland/chaparral
Habitat Comments: Clay soils in coastal sage scrub and grassland habitats at <300 m elevation. Mild disturbances may create local conditions appropriate for germination.
Economic Attributes Not yet assessed
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Management Summary Not yet assessed
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Population/Occurrence Delineation Not yet assessed
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Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 23Dec1991
NatureServe Conservation Status Factors Author: Annable, C., rev. Maybury (1997), rev. Gries (1998)
Element Ecology & Life History Edition Date: 15Jun1992

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
Help
  • Baldwin, B.G. 1999a. New combinations and new genera in the North American tarweeds (Compositae-Madiinae). Novon 9(4):462-471.

  • Ferris, R.S. 1960. Illustrated flora of the Pacific states: Washington, Oregon, and California. Vol. IV. Bignoniaceae to Compositae. Stanford Univ. Press, Stanford, CA. 732 pp.

  • Hickman, J. C., ed. 1993. The Jepson manual: Higher plants of California. University of California Press, Berkeley, CA. 1400 pp.

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Munz, P.A. 1974. A flora of southern California. Univ. California Press, Berkeley. 1086 pp.

  • Smith, J.P., and K. Berg. 1988. California native plant society's inventory of rare and endangered vascular plants of California. 4th edition. California Native Plant Society, Sacramento. 168 pp.

  • U.S. Fish and Wildlife Service. 1995. Proposed endangered status for four plants from southwestern California and Baja California, Mexico. Federal Register 60(153): 40549-40557.

  • U.S. Fish and Wildlife Service. 1998. Endangered and threatened wildlife and plants: determination of endangered or threatened status for four plants from southwestern California and Baja California, Mexico. Federal Register 63(197):54938-54956.

  • Wiggins, I.L. 1980. Flora of Baja California. Stanford Univ. Press, Stanford, California. 1025 pp.

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