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, these pocket guides to the twayblades and adder’s-mouths form part of a series that will cover all the wild orchids of the continental United States and Canada.      Brown provides 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 intriguing. For the twayblades and adder’s-mouths he includes information on 21 species, 1 additional variety, and 2 hybrids.      Most twayblades and adder’s-mouths are relatively small plants with tiny green flowers, but a few have richly colored blooms or particularly interesting habits that attract the native orchid enthusiast. Most of these species 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 plant with the striking photos in the backpack-friendly laminated guide should enable both professional and amateur naturalists to achieve the satisfaction of identifying a specific orchid.