This encyclopedia offers access to the diversity of ferns and seed plants, the most important groups of green land plants. Available information of general and systematic relevance is synthesized at the level of families. Evidence from virtually all disciplines important to modern taxonomy makes the work a most valuable source of reference not only for taxonomists, but for all who are interested in the various aspects of plant diversity. A revised classification includes a complete inventory of genera along with their diagnostic features, keys for identification, and references to the literature. The first volume deals with pteridophytes and gymnosperms.