The San Bruno elfin butterfly (Callophrys mossii bayensis or Incisalia mossii bayensis) is a U.S. Federally listed endangered

Endangered species

An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

 subspecies

Subspecies

Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

 which inhabits rocky outcrops and cliffs in coastal scrub on the San Francisco peninsula, endemic to this habitat in California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. Its patchy distribution reflects that of its host plant, Broadleaf Stonecrop (Sedum spathulifolium)

Sedum spathulifolium

Sedum spathulifolium is a species of flowering plant in the stonecrop family known by the common name broadleaf stonecrop. It is native to western North America from British Columbia to southern California, where it can be found in many types of rocky habitat in coastal and inland hills and...

.
Adults of this butterfly

Butterfly

A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured...

 emerge in early spring, in February and March, when nectar providing flowers open.