Trifolium amoenum

A distinct species in a genus of about 300 species, most abundant in north temperate regions.

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.

Historically in Alameda, Mendocino, Marin, Santa Clara, Solano, Sonoma, Napa counties, California; currently believed extant only in Marin (native) and Sonoma (reintroduced) counties.

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).

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).