Most succulents grow mostly in dry areas. Does that qualify them as xerophytes? Let’s find out together in this blog post!
Yes, succulents are xerophytes to an extent. Over time, most succulents have adapted to thriving in conditions with little water. But not all succulents are xerophytes. Some grow in water-abundant areas. Most notable examples include Echeveria and aichryson which originate in moist and cool forest areas.
When we talk about succulents as xerophytes, the focus is usually on the water storage bit. But it’s a little more than that. Succulents that qualify as xerophytes have a horde of other qualities that ensure the plants survive whatever their harsh habitat throws at them.
Let’s take a look at some of these properties.
Adaptations of Succulents as Xerophytes
Here are a few ways by which succulents have evolved to survive in the desert. Of course, specific species have their unique ways of staying alive. The adaptations below are those that tend to be common across various succulent groups.
Extensive Root System
The roots are usually the first to interact with water in a plant. To some extent, they determine just how much gets taken up.
In succulents, the roots must absorb as much water as possible as soon as it’s available – it’s going to be unavailable for a long time.
So you’ll find that most succulents have a spread-out and relatively shallow root system that enables them to trap rainwater immediately it hits the soil. Some succulents like certain species of cactus have an added twist.
As soon as the ground is a bit wet, they put out new temporary roots that increase the surface area of water absorption. Such roots dry up as soon as the rains stop.
The water is then stored thanks to various modified parts – mostly leaves and stems.
Water Storage Mechanisms
Water storage is actually the reason succulents are called so. The stems and leaves appear swollen because they have the secondary purpose of storing water for the plant. It’s that swelling that’s referred to as succulence.
This is because succulents don’t have the luxury of absorbing water when they need it – their habitat is drier than it’s wet. As mentioned, they absorb as much as possible once it hits the ground around them.
But they can’t utilize this water immediately since it’s quite substantial. On the other hand, the rains will be gone for a long time which means utilizing the water right away might not be the best idea.
So the water is kept in leaves and stems as the plant utilizes it bit by bit until the next downpour.
Stomata are important openings on a plant’s leaves and stems. They’re responsible for the intake of CO2 which is broken down in the process of photosynthesis to manufacture food for the plant.
Additionally, stomata also allow plants to lose excess water through the process of evapotranspiration. While it might be useful for lots of plants, evapotranspiration can end up hurting succulents.
Remember, they don’t have the excess water in the first place. They’re trying to hold onto as much of it as possible. Having so many let-outs for this water is a bit of a disadvantage. As a result, most succulents tend to have very few stomata – and they don’t even open them during the day thanks to the CAM mechanism (more details in a few).
Succulents can be quite glossy – especially if you’re taking good care of them. While the arid and semiarid succulents can’t get enough water, they get one thing in excess – the sun.
Of course, some love it. But that’s only to a particular extent. Sometimes the rays burn a bit too hot for comfort.
A reflective surface does help to bounce off some of that hence keeping the plant sane – and alive. In addition to the shiny surface, some plants are covered with hairs that are just as effective in bouncing off the light.
Other succulents also produce UV-absorbing compounds that are basically sunscreen, but for plants.
Finally, some succulents also turn red if exposed to too much sunlight as a coping mechanism.
Have A Cuticle
The reflective surface we’ve just discussed above is partly thanks to the cuticle, an outer covering on the leaves.
The cuticle is both thick and impervious, serving several functions concerning both the external and internal region of the leaf. But the most important one is about water loss.
Being thick and impervious, it helps lots of succulents hold onto water for long periods – just long enough before the next rains.
CAM is an abbreviation of Crassulacean Acid Metabolism, one of the most important adaptations in succulents.
In most plant species, both photosynthesis and gaseous exchange occur during the day when the sun is up. It’s also during this time that plants lose the most amount of water through transpiration which is perfectly fine in an environment with enough rainfall.
Succulents can’t afford to lose water this way – at least not during the day when temperatures are through the roof thus increasing the rate of evaporation. That’s exactly what CAM addresses.
Through the mechanism, the stomata remain open only during the night collecting CO2 – an important gas in photosynthesis. During the day, the stomata close, and the CO2 that was collected during the night is utilized in photosynthesis.
Some succulents take forever to mature. This is one of the main reasons why these plants got so popular.
The compact and slow growth makes them attractive to people who don’t have much space for rapidly-growing houseplants. That means they can fit into small spaces and stay there for a long time.
Turns out this is also an adaptation.
Growth is a water-intensive process and being in a dry area means potential problems if it were to go on at an unchecked rate. Sooner or later, the plant will run out of the important resource and, of course, die off as a result.
With slowed growth, succulents use little water for longer periods which keeps them going in areas they shouldn’t otherwise survive.
Presence of Spikes and Hairs
This is most notable in cacti species. The thorns are actually modified leaves that dramatically reduce the surface area available for evapotranspiration which preserves water.
But there is another way by which these spikes and hairs prevent water loss.
They create a small humid environment around the plant with more moisture outside than inside the plant. This is enough to reduce any would-be evaporation of water from the plant.
The spikes also provide a shade, by the way, that keeps the plant cool relative to the surrounding. Again, this ensures that as little water as possible leaves the plant through evapotranspiration.
Succulents – a big chunk of them – naturally grow in dry areas. They have all the adaptations to thrive there which makes them xerophytes. In fact, succulents got their name from one of these adaptations – storing water in their leaves and stems which gives the plants a fleshy appearance (succulence).
Some adaptations also make succulents the prized ornamental plants they are. For instance, the relatively slow growth by most of them makes them a favorite among houseplant lovers with little space to spare. Also, the ability of some to change color when exposed to too much sunlight makes them even more desirable.
But remember – not all succulents are xerophytes. Some are actually native to pretty moist areas so they have slightly different adaptations.
Hello! I’m Oscar, a freelance writer from Kenya. Among other topics, I also love writing about houseplants – succulents to be specific. I prefer them because they’re so much easier to care compared to other plants and they also offer so much variety in terms of shape, size, and color.