Camissonia benitensis

Camissonia benitensis
Conservation status
Threatened (ESA)
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Myrtales
Family:	Onagraceae
Genus:	Camissonia
Species:	C. benitensis
Binomial name
Camissonia benitensis P.H.Raven

Camissonia benitensis is a species of evening primrose known by the common names San Benito suncup^[1] and San Benito evening primrose. It is endemic to the Diablo Range of the South Coast Ranges of 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 almost always found growing on serpentine soils; however, at least 10 populations of the species are known to occur on greywacke substrates. Most of the habitat of the species is associated with the New Idria Serpentine Mass, Laguna Mountain Serpentine Mass, Hepsedam Peak Serpentine Mass, Panther Peak Serpentine Mass, Mustang Ridge Serpentine Mass, and numerous smaller serpentine masses between. These masses are surrounded by non-serpentine rocks of the Franciscan Formation, including greywacke which some populations of Camissonia benitensis occur. 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. Most nonserpentine soils have a ratio far greater than 1 (more calcium and much less magnesium). The extreme chemical characteristics of serpentine soils give rise to uniquely adapted and rare serpentine endemic plant species such as C. benitensis.

Like Camissonia benitensis, the previously ranked strict serpentine endemic Layia discoidea also has several populations that occur on greywacke and chert outcrops and talus around the New Idria Serpentine Mass. Additionally, the strict serpentine endemic Quercus durata var. durata also occurs on greywacke in the vicinity of Condon Peak adjacent to the New Idria Serpentine Mass. The occurrence of these strict serpentine endemics on graywacke suggests that greywacke has physical and or chemical characteristics similar to serpentine and may serve as a habitat analog.