Saguaro was originally Cereus giganteus, which means "giant column" and is related to a number of smaller, columnar cacti. In 1908, two cactus specialists from the New York Botanical Garden renamed it for Carnegie, who funded much of their research. Saguaros are icons of desert fauna. The University of Arkansas notes they only live in the Sonoran Desert of Arizona, Mexico, adjacent parts of California and the Baja Peninsula. Although they are easy to grow from seed, saguaros don't begin to branch until they are about 75 years old.
Sometimes, relatives appear very different, such as Aloe vera, known as common aloe and Kniphofia uvaria, commonly called Kniphofia or red hot poker, both of which are members of the Asphodelaceae family. Although both have poker-style flowers on tall spikes, Aloe vera's leaves are fleshy and serrated versus Kniphofia's grass-like leaves. Not all aloes have pulpy leaves. While torch lilies are mainly decorative, aloe vera often is grown for its medicinal properties. Its leaves contain a gel used topically to heal burns and other skin problems. Taken internally, the gel acts as a laxative. The Mayo Clinic website notes scientific evidence to support both uses.
Sempervivum tectorum is one of the most common succulents in the home garden. Sempervivum means "live forever" whereas "techtorum" refers to roofs. Historically, some cultures have grown these plants on house roofs, according to the website The Succulent Plant Page. Sometimes referred to as "house roof leeks," they are better known as "hens and chicks." As the rosettes formed by the petal-like leaves grow larger, they produce smaller offsets. It takes a few years for a rosette to flower, according to the Choosing Voluntary Simplicity website. Then, although the rosette "hen" dies, its "chicks" live on.