This edition is a reprint of Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie, Volume 119, and will be welcomed by most botanists and cactophiles of the world. It is based on herbarium material, on extensive field observations covering almost the entire area of the genus distribution, and on the study of cultivated specimens. It provides exhaustive information on this remarkable genus to anyone interested in the cactus family and its history, taxonomy, morphology, ecology, biology, and cultivation.