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A Cactus by Any Other Name

© Leigh SumnerKirk

Mention succulents at your next social gathering, and a predictable response is virtually guaranteed. On a rare occasion, you might get lucky and encounter unabated enthusiasm for exotic plants. More frequently, you will face the blank stare of non-comprehension, or possibly a dissertation on the respondent's favourite food. While probably unfamiliar with the intricacies of botanical nomenclature and terminology, most people do possess some knowledge of these unique plants. In fact, there are many succulents living contented, anonymous lives as houseplants.

What exactly is a succulent plant?

The term succulent refers to a plant that possesses some capacity for storing water. There are some notable exceptions, but these plants generally originate in arid regions. In order to survive in these extreme climates, many plants have developed characteristics that allow them to best utilise infrequent moisture accumulation. The most logical way to accomplish this is by hoarding as much water as possible while it is available, and this, indeed, is what the plants do.

To be considered succulent, a plant must exhibit this water storage characteristic in at least one of three different places: roots, stems, or leaves. Leaf succulence is instantly recognisable, demonstrated in the engorged quality of the plants leaves. Lithops, the popular "living stones" of Africa, are the ultimate example of this characteristic. These little plants have taken adaptive evolution so seriously that they now possess only a pair of leaves grown from a network of small roots. While the roots are responsible for gathering water, the two leaves store water and gather light for photosynthesis.

Similarly, stem succulence is manifested in the swollen nature of a plant's stems or branches. Some Cacti, particularly the types most people are familiar with, fit into this category. Saguaro, for instance, store water in their barrel-like stems and appendages. Like many other succulents, these Cacti have also transformed their leaves into spines as an adaptive measure. Plants with spines, which have less surface area than leaves, require less water and nutrients.

Root succulence can be the trickiest to diagnose. These plants accumulate water in underground storage tanks. Their tuberous roots, or caudexes, can reach baffling proportions. The caudexes are sometimes partially exposed naturally. In cultivation, growers often raise caudexes above the soil line for effect. Some root succulents, such as the vining plant Kedrostis africana, are literally Cucurbits-members of the gourd family (Cucurbitaceae), cousins to the common squash.

So what's the difference between a Cactus and a Succulent?

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