This book is about geology, soils, and plant communities in serpentine landscapes of western North America. Aspects of the interaction of geology and soils reveal a fascinating symbiosis relating the structure, composition, and distribution of plant communities. The plants that survive are a unique group. There are some entire genera or even families of plants that are common throughout California that are poorly represented on serpentine, while other genera are more diverse on serpentine than on other soils. Serpentine rocks have dramatic effects on the vegetation that grows on them. Many common plants cannot grow on serpentine soils, leaving distinctive suites of plants to occupy serpentine habitats. The floristic diversity associated with serpentine soils formed above ultramafic rocks is surprising considering that these soils are toxic to many plants. Serpentine barrens of California often look like moonscapes but here we find numerous species of plants of low biomass that produce a richness of species rarely found in the world.