Vegetation on ultramafic soils takes the form of distinctive variants of conifer-hardwood forest, chaparral, or grassland. A similar lessening of contrasts in S-NS vegetation was noted in the United Kingdom. Floras on ultramafic soils can be strikingly unusual. Also many NS taxa may be excluded from adjoining S soils. The greatest concentration of species endemic to serpentine is in the Klamath-Siskyou mountain complex of northwestern California and southwestern Oregon, with secondary concentrations in the North Coast and South Coast ranges and the Sierra Nevada of California.
Endemics belong to genera abundantly represented in the regional flora.
Indifferent or bodenvag species are often racially differentiated into tolerant and intolerant biotypes. The fauna on western North American serpentines has received but scant attention, and merits closer study. The evolution of a serpentine flora may involve a variety of speciational routes. This sequence is illustrated by Streptanthus, a genus of western North America crucifers, with varying degrees of fidelity and narrow endemism to California and Oregon serpentines. A more rapid mode of speciation on serpentine, saltational speciation by catastrophic selection, has been proposed.