Camissonia benitensis is a species of evening primrose known by the common name San Benito evening primrose. It is endemic to California, where its range includes far southern San Benito County, far western Fresno County, and far eastern Monterey County. The species is categorized as a strict serpentine endemic, meaning that it is always found growing on serpentine soils; however, at least four populations of the species are known to occur on shale substrates. Serpentine is an ultramafic rock. It weathers to produce soils with characteristically low levels of nutrients like nitrogen, phosphorus, potassium, and calcium, and high levels of magnesium and heavy metals including nickel and chromium. A major, consistent chemical feature of serpentine soil is a bioavailable calcium:magnesium ratio much less than 1.