Drs. Crosby and Allen, with help from colleagues in Costa Rica and Panama, will study the mosses of Central America in order to compile an illustrated identification guide to the estimated 1100 species of mosses in this tropical region. The moss flora will include descriptions of all known species, reliable keys for their identification, illustrations of diagnostic morphological features, and notes on their geographical ranges and habitats. The materials for this study comprise herbarium specimens collected in the past as well as new collections from poorly sampled areas in Central America, collected with the support of other funding sources. Computer facilities will be used in all aspects of the production of the resulting manual. Although individually, mosses are small, seemingly insignificant plants, they are important in retarding soil erosion, in providing seed-beds and habitats for soil invertebrates, and in other aspects of ecosystem processing of materials. They also are subjects of study into mechanisms of drought resistance and of pollution effects. Provision of a reliable manual for the identification of Central American mosses will facilitate such studies for tropical regions of the world. As well, such a manual will help stabilize the scientific nomenclature of these plants and provide data for assessing their historical biogeography.