Cactus comes from the Greek word katos. Cacti were well known to the Incas of Peru, the Aztecs of Mexico, and North American Indians long before their discovery by European explorers such as Columbus. An ancient Aztec myth recalls a vision by a priest in 1325 to build the Aztec capital where an eagle perched on a large cactus. That capital became Mexico City and the symbol of an eagle perched on a cactus is used on its flag today.
Cactus plants were introduced as curiosities in Europe as far back as the 15th and 16th centuries. They became very popular, leading to European collecting expeditions and extensive collections that peaked in the 1800's during the greenhouse craze. Today, there are impressive collections in both private and botanical gardens. Two of the best known are the Huntington Botanical Garden in California and the Royal Botanic Gardens in Britain. Cacti and succulents grow not only in desert terrain, but also in mountainous deserts and even jungle rainforests. The tallest freestanding cactus has a maximum-recorded height of 63 feet and the smallest a height of 0.4 in.
Cactus and succulents are valued not only for their unusual appearance as botanical specimens, but also as sources for food, drink, cosmetics, medicines, implements and construction materials. The succulent Agave provides tequila, Opuntia cactus is processed to make the food nopalitos, and Aloe sap is found in cosmetics and used to treat minor burns and wounds. Succulents such as Jade, Agave, and Aloe are grown for their striking appearance.
The terms cactus and succulent are often used interchangeably and can be confusing. A very simplistic description is that all cacti plants can be considered as succulents, but not all succulents are cacti. Succulent refers to fleshy tissue plants that include the cactus family. All succulents are able to store moisture in the fleshy tissue in their stems, roots, and leaves that have evolved and developed to reduce moisture loss and withstand often-hostile environments. Succulents also have the ability to go dormant, in severe adverse conditions.
Cacti are differentiated from other succulents by the manner in which they grow their familiar sharp spines. Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. Look closely at a cactus and you will see the spines growing from a point on their surface called an areole. A single spine or a cluster of spines grows out of this areole. Areoles are highly specialized. Cactus spines are easily detached, as you well know if you have ever been "stuck" by touching a cactus. Cactus areoles and spines can be tiny and thus not easy to see. Cactus spines vary widely in appearance and texture. Some are thick, sharp, short or long. Others can be softly curved, wooly, and wickedly barbed.
Succulents also differ from true cacti in that they grow their spines directly from stem tissue, often along the leaf margins rather than from areoles. Their spines usually are observed as singular spines rather than clusters, and do not normally detach. Just the same, they can stick you. Those spines can be very short, stout, sharp, and also barbed (I can attest to the accuracy of this statement since I have an unusual Agave with sharp leaf ends that attack any finger that gets too close.)
Cacti and other succulents can have beautiful flowers. See the photo accompanying this article. It is one of my cacti that bloomed this summer. Often because of their severe growing climates, cacti and other succulents flower, pollinate and develop seeds in shorter than usual time periods. Their flowers are varied in color, shape and size in order to attract pollinators. Once pollinated, the flowers develop into fruits containing seeds. Almost any fleshy cactus fruit is edible. Birds, animals and even man eat these fleshy cacti and succulent fruits.
Commercially, huge numbers of cacti and succulents are produced annually. They are very popular houseplants. Even "big box" stores are sources for unusual and inexpensive cactus and succulents. Cacti and succulents come in strong architectural forms and interesting textures. These are not demanding plants. Try collecting them.