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.
  
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• 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.