The district of Juxtlahuaca (approximately 4000 square kilometers) of the Mixteca region of northwestern Oaxaca state is characterized by a diversity of habitats ranging from tropical deciduous forest to moist tropical forest. Starting in the Summer of 1994, researchers at the IZTA herbarium of the National University of Mexico and The University of Texas herbarium (TEX) began an effort to document the flora of the district. Five thousand plant collections have been gathered and 18 new species described to date from these efforts. We estimate that approximately 2300 species of vascular plants are present in the district. Species diversity is equally divided among the three principal biomes in the region namely, the tropical deciduous forest, the pine-oak forest, and the cloud-tropical moist forest. The tropical deciduous forest of the northern part of the district is essentially similar in its composition to counterparts in other areas of Mexico with the interesting aspect being the plant diversity of the gallery forests of the Mixteco River. The tree layer of these gallery forests includes Aphananthe, Diospyros, Lysiloma, Quercus, Thouinidium, and Ulmus. The pine-oak forest is composed of seven species of pine and approximately 21 species of oak. The dominant trees of the cloud forest of the highest peaks in the south (2800 m) are Cinnamomum, Clethra, Cornus, Drimys, Eugenia, Ilex, Magnolia, Nectandra, several species of Quercus, Quetzalia, and Styrax. Information from all collections is kept in a database from which labels and other printed matter can be produced. All the collections have been georeferenced. This database will provide the basis for writing the flora of the district and preparing conservation initiatives to be implemented by local and federal government agencies.

Key words: District of Juxtlahuca, floristic inventory, Mexico, northwestern Oaxaca, specimen databases, tropical forest floristic composition