Introduction

Serpentine habitats in western North America have been recognized for their special geological, floristic, and ecological significance since the mid-20th century. Their intimate link with plate tectonics was established in the revolution that remade geological science. The occurrence of serpentines is not uncommon in the three Pacific Coast states (California, Oregon, and Washington) and in adjacent British Columbia, Canada. The uniqueness of biota on serpentines has commanded much attention. Their rich endemic floras and remarkable physiognomy, which contrasts with typical vegetation on adjacent soils, coupled with specialized ecophysiological attributes, have interested a variety of plant biologists from physiologists and taxonomists to population and evolutionary biologists. Comprehensive reviews of serpentine biology can be found in Proctor and Woodell (1975), Kruckeberg (1985), Brooks (1987), Baker, Proctor and Reeves (1992), Roberts and Proctor (1992).

This review focuses on an aspect of Pacific Coast serpentines that is one of the major themes of the present volume, namely barrens. The word barren and its companion word serpentine have taken on diverse meanings. Serpentine has been used adjectivally (and even as a noun) by botanists in a loose generic sense to stand for rock, minerals, soils, flora, vegetation, habitats, and even landscapes. For the geologist, the word embraces a family of ferromagnesian minerals, whereas serpentinite is used for a class of metamorphic rocks that contain serpentine minerals. The geological concept of serpentine will be considered later. However, the loose, all-inclusive meaning of serpentine is retained in this chapter.