Difference Between Cacti and Succulents

Cactuses and succulents share common traits, but cactuses belong to a distinct plant family within the succulent group. The word "succulents" is used for a group of plants capable of storing water, which makes them drought-tolerant. All cactuses are succulents, but not all succulents have the characteristics needed to qualify as cactuses.

Succulents are in more than 40 plant families that are grouped together because all their members store moisture in their stems, leaves or roots. The moisture-storage part of a succulent plant typically looks thick and fleshy. Succulents are native to most parts of the world, and many are used as garden plants and houseplants.

One example of a succulent is medicinal aloe (Aloe vera), which grows as a perennial plant outdoors all year in U.S. Department of Agriculture plant hardiness zones 10 through 12. This stemless, upright plant stores moisture in its thick leaves that contain a gel-like sap. Another succulent is the jade plant (Crassula ovata, USDA zones 11 through 12), which grows in a treelike shape and stores water in its stems and leaves.

Succulents common in outdoor gardens include hens-and-chicks (Sempervivum tectorum, USDA zones 3 through 8) and sedum, such as three-leaved stonecrop (Sedum ternatum, USDA zones 4 through 8). Both are low-growing succulents that spread readily in the landscape.

Cactuses have all the traits common to succulents and one additional characteristic: All cactuses have rounded, cushionlike parts called areoles; spines, hairs, branches, leaves and flowers grow from the areoles. Plants with areoles are in the Cactaceae plant family, and they are native to the Western Hemisphere. Most cactuses do not have leaves, and instead have prickly spines on their stems. Varieties that do not have spines may be smooth or scaled, or have hairlike growth on their stems.

Prickly pear cactus (Opuntia compressa, USDA zones 4 through 9) is native to many parts of the eastern United States. Its wide, modified stems are covered with areoles that hold thornlike spines. Some other cactus varieties, including bunny ears (Opuntia microdasys, USDA zones 8 through 11), have clumps of tiny spines growing from their areoles.

Cactuses grow in a wide variety of shapes and forms. Christmas cactus (Schlumbergera truncata, USDA zones 10 through 12) has a trailing form and is often grown in a hanging basket. Golden barrel cactus (Echinocactus grusonii, USDA zones 9 through 10) has a round shape and is covered with yellow spines. Cactuses also can have an upright, columnar form, such as the 10- to 14-foot-tall saguaro cactus (Carnegiea gigantea, USDA zones 9 through 10).