and Sonoma counties. Similarly, Macnab Cypress (Cupressus mac- 

 nabiana, Cupressaceae) is also generally, though not always, 

 found on serpentine. Clearly, neither of these tree species is a 

 serpentine endemic, although both of them usually occur on ser- 

 pentine soil. Next in line are species such as Knobcone Pine 

 (Pinus attenuata, Pinaceae) which frequently grow on serpentine, 

 but commonly occur on other soils as well. The fidelity of this 

 pine to serpentine is perhaps only about 50 percent. Next is a 

 species such as Jepsonia /zererfl^2G?ra,(Saxifragaceae) whose popu- 

 lations often occur immediately adjacent to serpentine rocks, 

 but rarely on serpentine. Only a few, rather unhealthy individuals 

 of this species are established on serpentine soil even though 

 abundant seed is dispersed to this soil type. Finally, there are 

 many plant species in California which never occur on serpentine. 

 Therefore, some species in the state's flora are true serpentine 

 endemics; others may be found on serpentine in some areas; and 

 still others are not known to occur on serpentine anywhere in 

 their range. 



Indicator Species 



The idea that certain plant species may be restricted exclusive- 

 ly to a single soil type or, by extrapolation, may occur in only 

 a certain climatic regime (such as does Coast Redwood, ^'e^/wow 

 sempervirens) brings up the concept of an indicator species. The 

 idea goes back to the American ecologist F. E. Clements, who 

 dominated the American ecological scene for many years. Al- 

 though many of Clements' ideas have fallen into disrepute 

 in recent years, he was an original thinker and made a number of 

 useful contributions to the development of ecological theory. In 

 Clements' words, the idea of an indicator species grows out of 

 the statement that "Every plant is a product of the conditions 

 under which it grows and is, therefore, a measure of environ- 

 ment." One can, as a consequence, state that a species such as 

 Sargent Cypress is an indicator of serpentine soil. The goldfield 

 Lasthenia minor subsp. maritima (Compositae) is an indicator 

 of seabird guano (Plate 4C). Cattails (Typha spp., Typhaceae) 

 are an indicator of prolonged (or permanent) flooding. The 



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