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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.〔(U.S. Department of Agriculture plant profile )〕 Specifically this rare species occurs in Napa,〔''Environmental Assessment for the Napa Valley Wine Train'' Napa County Planning Department and the California Public Utilities Commission, Earth Metrics report 10072, January, 1990〕 Santa Barbara,〔''Federally Listed Threatened & Endangered Species Which May Occur In Santa Barbara County, CA'' http://www.fws.gov/ventura/speciesinfo/spplists/sl_santabarbara_co.cfm〕 Solano, Contra Costa, Santa Clara, Monterey and Alameda Counties.〔(2004 Distribution map showing occurrences of ''Lasthenia conjugens'' )〕 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 present distribution is limited to the deltaic Sacramento Valley, principally Napa and Solano Counties,〔(''The Jepson Manual'', University of California Press 1993 )〕 but the historic range of ''L. conjugens''〔 is known to be significantly wider. In any case, historically the range has included parts of the North Coast, Sacramento Valley, and San Francisco Bay Area〔(Sensitive Species of the 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 implies that the plant actually prefers a theoretically drier environment, but is merely less successful than its competitors in surviving in drier (non-inundation) climate regimes.〔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〕
==Description==
''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 less than mid length, a distinguishing hallmark for identification of this species.〔(U.S. Federal Register Final Rule Listing Document (1997) )〕 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. According to Greene, the chromosome characteristic is: 2n=12.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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