When we use the phrase, "cacti and succulents," it is a bit of a misnomer. The phrase seems to imply that we are talking about two distinct groups that are on a roughly equal footing (in terms of botanical classification), as when we say, for example, "music and literature."
But all cacti are, in fact, considered to be succulents. That is, succulents are the overarching category; cacti are a sub-group of that category. And that is the most salient difference, such as it is, between cacti and succulents. So why does popular convention persist in using the somewhat misleading phrase "cacti and succulents," as if they were two different things altogether?
One can suppose that the persistence of this convention is attributable, in part, to the fame of cacti (the bigger ones, at least), which are well known even to people who have little interest in plants. Westerns turned cacti into iconic figures. Maybe the cacti then became so big for their breeches that they demanded equal billing with the plant category (namely, succulents) to which they belong. By contrast, many non-gardeners have no idea what a "succulent" is, botanically speaking, being familiar with that term mainly in a culinary context (as in, "Such and such is a succulent morsel"). Given this gap between the fame of the cactus and the relative obscurity of "succulent" as a botanical group, it easy to see why people might want to draw a distinction of convenience between them.
Maybe it also has something to do with the diversity of the succulent category. Somehow, it does not seem right that the lone word "succulents" should cover a whole group of plants ranging from the tiny "living stone" (genus Lithops) to the giant saguaro. Saying "cacti and succulents" may reassure us that we are acknowledging the scope of the intriguing (some would say downright weird) world of succulents.
Once you are introduced to succulents as a botanical category, it is usually relatively easy to pick them out from other plants. Because they tend to store water in their foliage and must be tough enough to survive challenging climates, most sport leaves or modified leaves that, while firm to the touch, have a swollen, "juicy" look (thus the name, "succulent") to them. Most cacti, of course, have spines (thorns), but not all do.
Examples of Succulents That Are Not Cacti:
Examples of Cacti:
View these pictures of cacti and succulents (including those in the Agave family) to determine if any of these extraordinary plants might prove useful to you as: