Cactus plants are prized for their exotic and dramatic shapes, textures and colors. Provided they are planted in a location where they can be admired but out of the way of bare-skinned swimmers, children and passers-by, cacti can be excellent choices for poolside landscaping. They also provide consistent color and form for patio, deck and porch container gardens. A tall, narrow cactus -- or any shape, for that matter -- can thrive on a city balcony or rooftop garden.
Here's where it gets tricky. Cactus plants -- or cacti, as they are known collectively -- are considered succulents, but not all succulents are cactus. True cacti have areoles -- from which spines, glochids, branches and flowers may sprout. Succulents, on the other hand, do not.
Parts of a Cactus
Spine: The sharp needle or thorn-like parts of a cactus plant that makes it prickly. Spines grow in clusters and are believed to have evolved from leaves. There are two types of spines: centrals, which are thicker or heavier and darker, and radials, which are usually straight and concentrated near the centrals. Spines also keep the plant from being consumed by most animals.
Areoles: Cactus flowers and branches originate from aeroles.
Cuticle: The outer layer of the epidermis, which is often waxy.
Tubercles: A small rounded projection or protuberance on the cactus plant.
Plants That Aren't Cacti
Some people call any desert-living plant a cactus. But, of course, they aren't. Let's look at the plants that are mistakenly referred to as cacti: