Carnegiea is a monotypic genus containing as its single species Carnegiea gigantea, commonly known as giant saguaro or saguaro cactus, which was originally named Cereus giganteus by botanist George Engelmann in the mid-19th century. Saguaros are found in the southwestern part of the United States (predominantly in Arizona and a limited number in California's Whipple Mountains) and in northwestern Mexico. If you don't live near a desert trail that takes you into cactopia, you may want to approach the prickly columns by saguaro surfing. (Ouch!)
Here are some links: Infos and references for your study tour and for your visual tour, I suggest the saguaro site of the School of Biological Sciences at the University of Edinburgh (no, the pictures were not taken in Scotland) and the George & Audrey Lange page.