Lasthenia conjugens
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 Lasthenia conjugens, Alameda County. Photo credit: John Game
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| Lasthenia conjugens |
Lasthenia conjugens, commonly known as Contra Costa goldfields, is an endangered species of wildflower endemic to a limited range within the San Francisco Bay Area of the state of California, USA.[1] Specifically this rare species occurs only in Napa,[2] Solano, Contra Costa, Santa Clara and Alameda Counties.[3] This annual herb typically flowers from March through June, and its colonies grow in vernal pool habitats at elevations not exceeding 100 meters above sea level. The Jepson Manual notes that the distribution is limited to the Sacramento Valley, principally Napa and Solano Counties,[4] but this characterization ignores somewhat recent recordings[3] in the other counties listed above. In any case, historically the range has included much of the North Coast, Sacramento Valley, and San Francisco Bay Area as well as the South Coast. Alternatively and less frequently this taxon has been referred to as Baeria fremontii var. conjugens.
Even though this plant is found almost exclusively in vernal pools, its behavior in controlled experiments indicates it prefers less than complete inundation. This impliies that the plant actually prefers a theoretically drier environment, but is merely more successful than its competitors in surviving seasonal inundation.[5]
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[edit] Morphology
Lastenia conjugens is an herb whose stems are simple or freely branched and erect, attaining a height of less than 40 centimeters. Their glabrous leaves, of length of approximately eight centimeters, are entire to pinnately lobed. Inflorescences appear in the form of solitary heads, with twelve to eighteen phyllaries fused at one third to mid length, a distinguishing hallmark for identification of this species.[6] An involucre structure measures six to ten millimeters and may be somewhat hemispheric. The receptacle presents as dome-shaped or obconic. The yellow ray flowers may number six to thirteen petals, and the five to ten millimeter ligules are yellow as well. The yellow disk flowers are numerous, and anther tips are linear to somewhat ovate. Style tips are triangular. The corollae are typically five-lobed. Style tips may be triangular or round, but typically hair-tufted. The glabrous club-shaped fruits are less than 1.5 millimeters across, black or gray in color, absent a pappus structure. The species is cross-pollinated.[7] According to Greene, the chromosome characteristic is: 2n=12.
[edit] Ecology
Lasthenia conjugens relies upon insect pollination for fertilization, and dispersal of seed is largely by gravity. Studies in Solano County natural and restoration habitats have shown variability between visitation rates to the two types of colonies; however, plant propagation rates were found to be similar between natural colonies and introduced ones, implying pollination is not a limiting factor of propagation.[8] An alternative conclusion is that members of one particular insect family, Sciaridae, are extremely efficient pollinators of L. conjugens, since it was the only insect family to visit the restoration colonies in significant numbers.
[edit] Conservation
Contra Costa Goldfields has been studied extensively with regard to genetic diversity of colonies. Some early findings were that repeated seedings in restoration colonies enhanced the resultant population of Lasthenia conjugens and hence ultimate survival.[9] The subsequent finding has been made that genetic diversity has been able to be replicated for introduced colonies in a restoration environment, implying favorable long-term stability and viability for introduced colonies.[10]
In addition to the federal status as an endangered species it gained on June 18, 1997, Lasthenia conjugens is acknowledged and protected under the Solano County Habitat Conservation Plan.[11]
[edit] See also
[edit] References
- ^ U.S. Department of Agriculture plant profile
- ^ Environmental Assessment for the Napa Valley Wine Train, Napa County Planning Department and the California Public Utilities Commission, Earth Metrics report 10072, January, 1990
- ^ a b 2004 Distribution map showing occurrences of Lasthenia conjugens
- ^ The Jepson Manual, University of California Press 1993
- ^ Gerhardt, Fritz and Sharon Collinge, Causes of rarity in the vernal pool endemic "Lasthenia conjugens" (Asteraceae), ESA August 5, 2003, Session # 36: Rare, Threatened, and Endangered Species Plants
- ^ U.S. Federal Register Final Rule Listing Document (1997)
- ^ Ornduff, Robert (1966). "A biosystematic survey of the Goldfield genus Lasthenia (Compositae: Helenieae).". University of California publications in botany 40: 1–92. ISSN 0068-6395, LCCN 66-64336.
- ^ Ramp, Jennifer M., Pollination and seed set of the endangered vernal pool annual "Lasthenia conjugens" (Asteraceae), Botany 2004, Ecology Section
- ^ Collinge, Sharon, Testing community assembly theory in vernal pool restoration, ESA, August 6, 2002, Session #32: Testing Ecological Theory in Restoration Practice
- ^ Jennifer M. Ramp, Sharon K. Collinge1 and Tom A. Ranker, Restoration genetics of the vernal pool endemic Lasthenia conjugens (Asteraceae), Conservation Genetics, Volume 7, Number 5, Pages 631-649, October, 2006, Springer Netherlands, DOI:10.1007/s10592-005-9052-2
- ^ Solano County Habitat Conservation Plan
