Regularity: Regularly occurring
Localities documented in Tropicos sources
United States (North America)
Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.
Global Range: Historically in Alameda, Mendocino, Marin, Santa Clara, Solano, Sonoma, Napa counties, California; currently believed extant only in Marin (native) and Sonoma (reintroduced) counties.
Comments: Typically in low, wet swales in grasslands. Also on grassy hillsides at up to about 400 m elevation. Per the California Dept. of Fish and Game (2000): Open, sunny sites, sometimes on serpentine soil in coastal bluff scrub and valley and foothill grassland; most recently seen on a roadside that had been graded and on an eroding cliff face. Possibly requires disturbance-created openings for germination.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 1 - 5
Comments: Had been thought extinct until the early 1990s. A single plant was found in 1993 at a site in Sonoma County, but that site has now been developed and the species is considered extirpated there. However, seeds were collected from the plant prior to its extirpation and were subsequently multiplied. In 2006, some of those seeds were used to establish experimental populations at two sites in Sonoma County and at several sites at Point Reyes National Seashore (Marin County). It is as yet unknown whether any of the experimental sowings will persist (USFWS 2007). Another population, the only native population currently extant, was discovered in 1996 in Marin County. In 1997, seed from those plants was used to establish a small experimental population (approximately 20 seedlings) at Bodega Marine Laboratory (Sonoma County) (USFWS 2007). The Bodega experimental population had persisted as of 2007, but its long term fate is unknown (USFWS 2007).
Life History and Behavior
Mating system appears to include both cross-and self-pollination, as extant plants were found to have a higher level of heterozygosity than would be expected in a predominantly self-pollinating species (Knapp and Connors 1999 cited in USFWS 2007).
Date Listed: 10/22/1997
Lead Region: California/Nevada Region (Region 8)
Listing status: E
For most current information and documents related to the conservation status and management of Trifolium amoenum, see its USFWS Species Profile
National NatureServe Conservation Status
Rounded National Status Rank: N1 - Critically Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G1 - Critically Imperiled
Reasons: Formerly known from about 25 sites in 7 counties along the central California coast, this species was believed extinct until 1993, when a single plant was rediscovered in Sonoma County. That site has now been developed and the species is considered extirpated there. Another population, the only native population currently extant, was discovered in 1996 in Marin County. Seeds from both of these sites were used (separately) to establish experimental populations between 1997 and 2006; the long-term fate of those sowings is uncertain. The Sonoma and Marin plants differ in their morphology, so establishment/conservation of both forms is important. After stability/increase 1997-2005, the native Marin population declined sharply in 2006; it is unclear whether and when it may recover its former numbers. Some experimental sites sown with seed of the Sonoma plant appear to have failed, but others have apparently established and are increasing. Loss of habitat to urbanization and agriculture was likely the primary reason for the extirpation of so many populations, and this habitat loss in continuing within the species' historic range, limiting the number of potential reintroduction sites. The extant native population is on private land, where threats include development, gopher grazing, potential erosion and trampling, and non-native plants.
Global Short Term Trend: Decline of 10 to >90%
Comments: At the single remaining native population, there is high interannual variability in number of plants and in seed production (USFWS 2007). Population status was rated as stable or increasing through 2005 with high seedling densities in some years (Peter Conners pers. comm. June 2003), but a sharp decline was observed in 2006. Compared to 2005, in 2006 seedling number had declined by 94% and seed productivity had declined by 98%; seed production was the lowest of the entire 10-year monitoring period with low plant numbers as well (Connors 2006 cited in USFWS 2007). It is too soon to know whether this sudden decline will continue, or whether the population will recover. In 2005, a few plants were identified about 500 meters north of the main population, five of which set seed; however, no plants were found at the northern site in 2006 (Connors 2006 cited in USFWS 2007). The Bodega Marine Laboratory experimental population is not routinely monitored, although it appeared to experience a decline similar to that of the native population between 2005 and 2006 (Connors 2006 cited in USFWS 2007). At the other experimental sites, germination has been documented at most (USFWS 2007). Of the sites planted at the Point Reyes National Seashore, some have failed, but others appear to have successfully established and are increasing (J. DiGregoria pers. comm. 2009).
Global Long Term Trend: Decline of >90%
Comments: Historically known from 25 sites but probably extirpated at all but 1 of these (although some viable seed may remain in seedbanks and may germinate if conditions are right). Loss of habitat to urbanization and agriculture was probably the primary reason for the extirpation of so many populations. Even since 1997 when this species was listed as Engandered, much habitat potentially suitable for restoration has been altered and is now unsuitable due to urbanization, agricultural operations, and changes in the biological community and hydrological conditions (USFWS 2007).
Degree of Threat: Very high - high
Comments: Threats in the past were obviously very high, with habitat being lost to urbanization, agriculture, and (possibly) cattle grazing and/or competition from weedy non-native plants. Widespread urbanization continues throughout this species' historic range, and its current extreme rarity makes it precarious. Urbanization and agriculture may be preventing re-establishment of the plant from seed banks at historically-occupied sites (USFWS 2007). The single native population is located on private property in a developed area, and a house has recently been constructed within 100 feet of it. Future development plans on this property are not known. Gopher grazing is also a threat at this site and appears to have caused substantial recent mortality (USFWS 2007). This population is somewhat threatened by erosion because of its proximity to a coastal bluff, and could also be impacted by any potential expansion or increase in use of a small trail that runs through it to provide local homeowners with bluff access (USFWS 2007). Several non-native invasive plants, including Carpobrotus edulis, Lolium multiflorum, and Plantago lanceolata, are also present at this site and pose a potential threat (USFWS 2007). The Bodega Marine Laboratory experimental population is still very small and is located near heavily used buildings, although it is signed to prohibit unauthorized entry and reduce unnecessary foot traffic (USFWS 2007). Non-native plants including Medicago polymortha, Plantago coronopus, and Plantago lanceolata also occur in close proximity; laboratory staff currently mitigate this threat by weeding (USFWS 2007).
Biological Research Needs: Seeds of both the prostrate coastal form (from native population in Marin County) and the upright inland form (from now-extirpated plant in Sonoma Coutny) have been multiplied (to 20,000 and 50,000 seeds respectively) and are stored at several facilities for reintroduction and research purposes (USFWS 2007). Although the single individual found at the Sonoma County site had a relatively high degree of genetic variability, the reduction in number of extant individuals clearly represents a loss of genetic variability compared to what must have been present in the original population (USFWS 2007).
Names and Taxonomy
Comments: A distinct species in a genus of about 300 species, most abundant in north temperate regions.