Succulent Adaptations
By Andrea Peck
It's that time of year again. The hills are fading into a fawn-like color. The verdant green has passed and our high hopes that this year will certainly be the year that fills our water cups is looking unlikely. Those of you who see the glass as half full have trained your eye away from the lush tropical jungle of your dreams and towards the most logical gardening solution: succulents. It's true that succulents have many redeeming features, but it is their handy knack for tolerating our less-than-stellar rain totals that brings us back to them time and again.
Succulents are a loosely defined group of plants that, simply stated, are able to respond to a dry environment by conserving water. Originating in areas, such as deserts, where lack of water and extreme heat and sun can wilt the best of plants, survival depends on the ability to store and “guard” water. Most succulents have thick leaves or stems that contain specialized cells that retain water when rain or irrigation is plentiful. Almost any plant that exhibits this propensity falls under the label 'succulent.' Interestingly, that includes the cactus family. In fact, cacti are succulents, though, succulents may not always be cacti.
You can spot a succulent by its generally ample, fleshy body. The leaves or the stem are built for water retention. Some plants have an accordion-shape which acts like elastic, stretching or contracting and allowing the plant to fill or shrink based on water availability. This folding shape also reduces sun exposure. Some plants grow tall which essentially allows them to create their own shade.
Many succulents have a waxy outer-coating that further prevents water loss. The waxy coating does not cover the stomates, however. Stomates are openings, like pores, that allow carbon dioxide in and oxygen out. Because stomates are openings, they also have the potential to allow water out. Luckily, the finely-tuned succulent has an answer for that. Succulents, unlike other plants, open their stomates during the night—when heat and dryness are minimal. Conversely, they close their stomates during the day—again another stab at water conservation. This is called CAM photosynthesis and, though it is a neat trick, it is a less efficient use of energy in comparison to the method used by other plants. This is one reason that succulents tend to be slow growing.
The leaves of succulents are also an adaptation. Most succulents have less leaves, some have no leaves, and others have spines. Having less leaves limits the surface area that is exposed to the sun. Cacti actually photosynthesize through the stem. Spines are modified leaves, but do not serve a “leaf” purpose. Instead, they protect the plant from thirsty herbivores and provide shade. Some spines are so thick and hair-like that they create a pocket of insulation which keeps the plant cool, moist and protected from the elements. Light-colored stems and spines are another important adaptation because they reflect heat away from the plant.
You may have already noticed in your own garden, that succulents have shallow roots. Sometimes a plant may have a tap root as well, which helps keep the plant in one place. Shallow roots are advantageous for picking up any bit of rain that happens to be in the vicinity.
Perhaps one of the most interesting facts that I learned while reading about succulents is that some, such as the organ pipe cactus, grow underneath a “nurse” tree. The plant seeds and germinates there, all the while taking advantage of the cooling shade. But, as it grows and its root system spreads, the cactus dominates the area, taking in so much water that the nurse plant eventually dies.
Despite that gruesome tidbit, succulents remain a great garden solution for dry times. Their unusual shapes, colors and statuesque height can bring real drama to your garden. Just make sure you watch for spines and don't fret if you forget to water them and they look dead. They probably are just all pinched up waiting for a good rain—kind of like the rest of us.