Comprehensive quintessential reference book of cactus descriptions. It is THE essential and most complete description guide.
Quote in the introduction from the translators to English from German (High Wycombe and Lois Glass) "Backeberg created innumberable small genera ("splitting") in conformity whith his principles of classification and this runs strongly against the current of present-day thinking where the larger genus ("lumping") is preferred. "
Previous quote notwithstanding a serious collector/grower or student of cactus shouldn't ignore this work. I have used it for 29 years, my copy is frayed and I am about to spend the money for a fresher binding. It is the most reliable and complete reference on all Genera, specie and ssp of cactus.
It contains dozens of color photos taken in the mid-1960s primarily from specimen in European collections. However, its primary value lies in its descriptions, classification and tracing of taxonony science up through the mid-1960s.
The trend toward lumping has continued to a degree that current taxonomy in the botanical science has parted from the horticultural terminology in use by many of the serious commercial growers, vendors and collectors. Backeberg's classification system helps mitigate the differences.