This is a compilation of the flowering plants in an area comprising the island of Puerto Rico and the smaller islands belonging to the political unit of the Commonwealth of Puerto Rico. It includes all the native (endemic or otherwise) and naturalized plants in the area. The families have been numbered to provide a convenient guide to the user, and will be treated in numerical sequence as far as possible. After the description of each family, there is a key to the genera, followed by the treatment of each genus in alphabetical order, then by a key to the species within the genus, and descriptions of the species. Each description is followed by a short ecological note, the geographical distribution both within the area and worldwide, and their vernacular names, in both Spanish and English.