Most people who do not live in a desert environment consider cactus to be an unattractive species. Nothing could be farther from the truth, cactus are a beautiful species, similar to euphorbia in Africa. Euphorbia can be found all over the world. The forms range from annual plants laying on the ground, to well developed tall trees. In deserts in Madagascar and southern Africa, convergent evolution has led to cactus-like forms where the plants occupy the same ecological niche as cacti do in deserts of North America and South America. The genus is primarily found in the tropical and subtropical regions of Africa and the Americas, but also in temperate zones worldwide. The 1,500 to 1,800 species of cacti mostly fall into one of two groups of “core cacti”: opuntias (subfamily Opuntioideae) and “cactoids” (subfamily Cactoideae). Most members of these two groups are easily recognizable as cacti. They have fleshy succulent stems that are major organs of photosynthesis. They have absent, small, or transient leaves. They have flowers with ovaries that lie below the sepals and petals, often deeply sunken into a fleshy receptacle (the part of the stem from which the flower parts grow). All cacti have areoles highly specialized short shoots with extremely short internodes that produce spines, normal shoots, and flowers. In Las Vegas we have one of the best cactus gardens in the world at the Ethel M Botanic Garden.
At the Larco museum in Peru, they had a collection of the most unusual cacti I have ever seen. Earlier in cactus taxonomy, Cereus was a name that had been applied to nearly all known cactus species that were ribbed, columnar plants. Many of these plants have since been moved out into separate genera. Consequently, the 30 or so plants that remain in the Cereus group are largely plants that have not been moved out of the genus rather than plants that have been included because they fit the description of Cereus. This inclusion-by-lack-of-exclusion makes for a very messy and unsatisfactory grouping. The name Cereus peruvianus has been applied to both C. hildmannianus and C. repandus which are both recognized as legitimate species today. The trouble is, neither of them resemble the many plants that we see labeled as Cereus peruvianus.