The question of whether all succulents are cacti is a common point of confusion. The simple answer is no; all cacti are technically succulents, but not all succulents are cacti. This relationship is based on botanical classification. Succulents are defined by a broad physiological trait, while cacti are defined by a single, specific anatomical feature. Both groups survive in dry environments by developing specialized tissues for moisture retention.
What Defines a Succulent
The term succulent is a descriptive, functional label, not a formal taxonomic classification. It describes any plant adapted to store water in thickened, fleshy parts, such as leaves, stems, or roots. This adaptation allows these plants, often called xerophytes, to survive prolonged periods of drought in arid climates. The water-storing tissues can hold a significant amount of moisture. Succulent plants are found across more than 60 different plant families, showing that this trait evolved independently multiple times.
Cacti: The Specialized Succulent
Cacti are a specialized subset of succulents belonging exclusively to the plant family Cactaceae. This family is native almost entirely to the Americas. Classification into the Cactaceae family depends on one mandatory anatomical feature: the areole. The areole is a small, cushion-like structure appearing on the surface of the cactus stem. All spines, hairs, flowers, and new branches on a true cactus must emerge from this areole, making it the definitive diagnostic marker for the family.
How to Tell the Difference
Distinguishing a true cactus from another type of succulent relies entirely on locating the areole. On a cactus, the areole appears as a slightly raised, fuzzy, or woolly bump from which clusters of spines radiate. If a plant has spines or thorns but lacks this specialized, cushion-like growth point, it is a succulent, but not a cactus. Many non-cacti succulents, such as Agave or Aloe, store water in large, fleshy leaves that grow in rosettes. These plants may have sharp spines or teeth along the leaf margins, but these are part of the leaf structure and do not emerge from an areole. The presence of true, well-developed leaves is a strong indicator of a non-cacti succulent, as most cacti have reduced their leaves to spines to minimize water loss. The Euphorbia genus often causes confusion because many species resemble cacti with ribbed, spiny stems. However, the spines on a Euphorbia grow directly out of the stem tissue, often in pairs, rather than clustering within an areole. Inspecting the growth points for the presence or absence of the areole remains the most reliable method to determine if a plant is a member of the Cactaceae family.