Chaparral extends over most of the hills and lower slopes of California. Like all Mediterranean type vegetation, it has winter active and summer dormant phases, but the principle genera, Adenostoma, Arctostaphylos, Ceanothus, Heteromeles and Rhus are absent from other regions having a Mediterranean climate.  It has been postulated therefore that the Californian chaparral evolved in situ, and has over the period of its development given rise to over 24 endemic species.  Chaparral can be divided into about eight vegetation types. The main type is often composed of dense thickets of chamise Adenostoma fasciculatum. Associated endemics may include Elymus condensatus (Poaceae) and Erigonum fasciculatum (Polygonaceae).  Ceanothus chapparral is often the climax formation in northern California and may be dominated by several Ceanothus species such as C. crassifolius, C. oliganthus or C. thysiflorus. In the areas between Ceanothus shrubs, endemic species such as Artemisia californica (Asteraceae) may be present. On the many slopes, scrub oak chaparral is often conspicuous usually dominated by Quercus dumosa.  It is one of the most species rich forms of chaparral often supporting a large variety of associates such as Ceanothus leucodermis, Cercocarpus betuloides, Heteromeles artutifolia and the endemic Rhamnus californica (Rhamnaceae).

A less extensive chaparral is dominated by manzanita (Arctostaphylos species), which tends to be restricted to deeper soils especially at higher elevations. The characteristic species include Arctostaphylos manzanita and various endemics of this genus such as A. canescens, A. stanfordiana, A. tomentosa and A. viscida (Ericaceae). At higher altitudes, a ground-hugging, compact form of chaparral can be found supporting species such as Arctostaphylos nevadensis, Castanopsis sempervirens, Cercocarpus ledifolius, Chrysothamnus nauseous, Prunus virginiana and a variety of Ceanothus species. In the north this can extend up to the ponderosa pine forest where endemic such as Ceanothus fresnensis and C. prostratus (Rhamnaceae) occur, while in more southern areas the endemic Fremontia californica (Malvaceae) is more likely to be encountered.

A less common form of chaparral is dominated by the endemic red shanks Adenostoma sparsifolium (Rosaceae). This is often regarded as the most attractive form of chaparral, but is confined to just four locations in southern California and Baja California. Associated taxa include Adenostoma fasciculatum, Rhus ovata and several Ceanothus species. On the serpentine soils such as in the Coast Range and the foothills of the northern Sierra Nevada, a special type of chaparral can be found supporting a variety of localised endemics such as Arctostaphylos viscida (Ericaceae) and Ceanothus jepsonii (Rhamnaceae).

Finally in desert chaparral the dominant species often include endemics such as Juniperous californica (Cupressaceae) and Quercus turbinella var. californica (Fagaceae). Other endemics associated with Californian chaparral include Apiastrum angustifolium, Arctostaphylos elegans, Bloomeria clevelandii, Bloomeria crocea, Ceanothus dentatus, Chorizanthe californica, Chlorogalum pomeridianum, Corethrogyne filaginifolia var. bernardini, Cryptantha torreyana, Delphinium californicum, Dendromecon rigida, Emmenanthe penduliflora, Encelia californica, Eriophyllum lanatum var. achillaeoides, Eriophyllum confertiflorum, Filago californica, Garrya congdoni, Gilia capitata, Gilia clivorum, Gnaphalium californicum, Leptodactylon californicum, Lomatium lucidum, Madia gracilis, Marah fabaceus, Paeonia californica, Papaver californicum, Perezia microcephala, Phacelia imbricata subsp. patula, Pickeringia montana, Rafinesquia californica,  Romneya coulteri, Sanicula crassicaulis, Scrophularia californica and Silene californica.            

References

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