A much welcome field guide to 436 species of flowering plants, featuring McCullen's own color photographs, an overview of ecology and habitats, and an extremely useful botanical checklist by visitor site. While not nearly as celebrated as Darwin's finches or the sea-going iguana, the divergence of plants such as the endemic prickly pear cactus or Scalesia (an endemic genus in the daisy family with 15 species) in Galapagos, is just as interesting and important. A full page is devoted to each species, including a detailed description, habitat, distribution, a color photograph and comments on ecology, history and identification. Organized according to growth form, leaf pattern and flower color -- and bristling with botanic terms -- this is a long-awaited essential guide for those of us interested in plants. It's intended not just for botanically minded visitors but also for naturalist guides, residents and researchers.  (GPS40, $31.50)