California is well endowed with a widely diverse selection of indigenous plants. The highly varied topography and range of elevations in California are responsible for this abundance. When combined, these conditions create many climate zones and habitat areas that produce more than 6,400 native plant species. This range of flora is adapted and organized into many plant communities that thrive in specific climate zones from maritime to mountainous.
A comprehensive climate map of California was developed by the University of California Cooperative Extension, Division of Agriculture and Natural Resources (CCANR). This map, the Generalized Plant Climate Map of California, was published in the 1989 edition of the Sunset Western Garden Book. The map illustrates 24 different climate zones in California and is primarily based on annual high and minimum temperature ranges that define each zone. This map continues to be refined and revised with each new edition of the book and serves as a standard reference for both native and exotic plant selections.