What makes an orchid an orchid? On what basis are the 25000 species of orchids placed into genera? The exquisite colour illustrations and descriptions answer these questions in a detailed but jargon-free style. The botanically accurate plates illustrate the distinguishing generic characters in a set format, for simple comparison between genera. The Sheehans explain the basis of orchid taxonomy, describing the characteristics common to all orchids. There follows descriptions and depictions of 154 genera. This includes the distinguishing characters, major floral details, vegetative habit of typical species, and a list of popular species with flowering season and approximate native locale. An extensive, illustrated glossary describes more than 400 important terms. An important reference for professionals and the historical data and cultural requirements will be highly useful for the amateur.