Australia is about the size of the continental United States, with a population of around 15 million, roughly half that of California. About half the continent has a climate which could be called Mediterranean to some degree. In the western and southwestern regions of Western Australia and the Grampians Mountains of the southeastern corner, where the plant diversity is highest, the climate resembles that of Central California very closely. In this catalogue we have made an effort to list the origin of the plants for those who know or are learning about the biogeography of Australia. The northern regions of Australia are similar to our southern states in climate, except that northern Australia is deeply tropical.
Occasional rain is common there during the summer.
Overall, however, the climate is still Mediterranean in nature. The lower half of Western Australia has a climate that is very similar to that of Central or Southern California. Winters are somewhat wetter and warmer. Perth gets an average of about 40 inches of rain a year, and civic landscapes commonly include cultivars of Pimelea ferruginea and Chamelaucium uncinatum, plants which would not survive in many areas in California without winter protection. In all areas, the farther away from the coast one gets the hotter the summers become and the colder the winters will be.