Overview
White-rayed pentachaeta is a small, daisy-like annual plant in the aster family (Asteraceae) found only in San Mateo County. It is found on grasslands with serpentine soil.
Historically, the white-rayed pentachaeta was known from at least nine locations in Marin, San Mateo and Santa Cruz counties; however, most of the occurrences were lost due to urbanization or disturbance from off-road vehicles. At the time of listing, a single population of white-rayed pentachaeta was known in San Mateo County in an area called the Triangle, which is just west of Edgewood County Park and Natural Reserve. Currently, the Triangle population is covers 8.5 acres in the Triangle proper and 13.5 acres across Interstate 280 in Edgewood County Park for a total of 22 acres. The population here is estimated at approximately 1.5 million plants. A small, second population estimated at 300 to 3,000 plants was also verified in 2018, growing on the west side of the Upper Crystal Springs Reservoir.
This species was listed as endangered on February 3, 1995.
The plant continues to be threatened by:
- Drought and flooding due to climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.
Learn more about climate change - Nitrogen deposition due to exhaust from I-280
- Non-native and woody plant encroachment
- Lack of redundant populations
Only two populations are known, and most plants of the species are located on a portion of one of those two areas. This leaves the species susceptible to catastrophic events in that location.
Scientific Name
Identification Numbers
Characteristics
Similar Species
Habitat
White-rayed pentachaeta grows in serpentine soil grassland between 120 to 2,000 feet. Serpentine soil is a high magnesium, low nitrogen soil that tends to restrict the growth of most plants, which helps to reduce competition for space, water and sunlight.
Land on which the natural dominant plant forms are grasses and forbs.
Physical Characteristics
White-rayed pentachaeta is a small annual plant of the aster family (Asteraceae) with one or a few branches that have narrow, linear leaves. The plants are 2.3 to 6.6 inches tall. Each daisy-like flower head has 16 to 38 very small yellow flowers in the central disk area, and 7 to16 ray flowers around the disk, each with one white or purplish petal.
Life Cycle
White-rayed pentachaeta flowers from March to May and may be visited by the federally threatened
bay checkerspot butterfly (Euphydryas editha bayensis). The butterfly may incidentally pollinate the plant, but the primary pollinators of white-rayed pentachaeta are unknown. The species may have a limited soil seed bank due to the seeds not overwintering well. As is common among annual plants, white-rayed pentachaeta population size fluctuates dramatically from year-to-year.
Geography
Historically, the white-rayed pentachaeta was known from at least nine locations in Marin, San Mateo and Santa Cruz counties; however, most of the occurrences were lost due to urbanization or disturbance from off-road vehicles. At the time of listing, a single population of white-rayed pentachaeta was known in San Mateo County in an area called the Triangle, which is just west of Edgewood County Park and Natural Reserve. Currently, the Triangle population is covers 8.5 acres in the Triangle proper and 13.5 acres across Interstate 280 in Edgewood County Park for a total of 22 acres. The population here is estimated at approximately 1.5 million plants, almost all of which are in the Triangle proper. A small, second population estimated at 300 to 3,000 plants was also verified in 2018, growing on the west side of the Upper Crystal Springs Reservoir.
Timeline
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