Native orchids are increasingly threatened by pressure from population growth and development but, nonetheless, still present a welcome surprise to observant hikers in every state and province. Compiled and illustrated by long-time orchid specialist Paul Martin Brown, this pocket guide to the woodland and bog rein orchids forms part of a series that will cover all the wild orchids of the continental United States and Canada.            Brown provides a description, general distributional information, time of flowering, and habitat requirements for each species as well as a complete list of hybrids and the many different growth and color forms that can make identifying orchids so challenging. For the woodland and bog rein orchids, which make up some of the most delicate and subtly colored of all wild orchids, he includes information on nineteen species, four subspecies and varieties, and seven hybrids.      The genus Platanthera is the largest genus of orchids to be found in North America north of Mexico; the woodland and bog rein orchids comprise a significant group of species found throughout much of temperate U.S. and Canada. The luminously green rein orchids, so-called because of the resemblance of some of the flowers to the reins used on horses, are especially abundant in rich woodlands, wetlands, and bogs in the more northerly and cooler habitats. Most are easy to identify based upon their general appearance, range, and time of flowering. Answering three simple questions-when, where, and how does it grow?-and comparing the living plants with the striking photos in this backpack-friendly laminated guide and the information in the simple key should enable both professional and amateur naturalists to achieve the satisfaction of identifying a specific orchid.