Leaves are an important part of a plant because they perform the vital process of photosynthesis, a function of processing and storing food, that helps the plant to survive. However, cacti don't necessarily have a lot (if any) leaves. So, where and how does a cacti perform the process of photosynthesis in order to survive?
The Cactus Family
The Cactaceae botanical family contains over 2,000 species of cacti; the majority of these species are found in dry, desert areas of the world such as Australia, East Africa, the southern Mediterranean area, Central and South America and the South Western states of the United States. Many of these areas have little or no rainfall, making it extremely difficult for the average plant to survive.
Cacti grow in a wide variety of shapes, sizes and colors; many cacti have colorful blooms during flowering season. In order to function and flourish in such an environment, cacti have learned to adapt and process vital life food differently.
Cacti have adapted the normal structures found on a plant to cope with their environment. A cactus is made up of a stem, the skin, roots, areoles (new growth of spines and flowers) and spines. The spines (leaves) of a cactus are discussed below, as is the stem of the cactus in relation to photosynthesis.
Spines and Leaves on Cacti
According to the School of Biological Sciences at the University of Texas website, some species of cacti have both leaves and spines, although it is the predominant spines that you notice first and any leaves that a cactus may have are of little consequence (in the process of photosynthesis). Spines of a cactus are sometimes referred to as the leaves of the cactus, but they do not perform the same function as leaves on a regular plant.
Cacti spines are located in the axil of the cactus leaves in clusters (sometimes these are so small that you barely notice them). The School of Biological Sciences at the University of Texas website describes the spines of a cactus as “modified leaves or modified bud scales.” However, spines do not necessarily carry out the same function as leaves on a regular plant; spines perform the following functions:
- protection against predators
- water collection (in some species)
- maintain a lower temperature for the cacti by helping to reflect light away from the stem.
(source: Cactus Museum.com: Cactus Survival)
The Crassulacean Acid Metabolism Method in Cacti
Most plants perform a process of photosynthesis through the stomata in the leaves of the plant; the process of photosynthesis helps a plant to make and store food for its survival. However, cacti have developed a different process of “photosynthesis” which takes place inside the stem of the plant and not the leaves. Therefore, the absence of leafy leaves on a cactus is not as important as you might think in the process of survival; if a cactus has little or no leaves (as oppose to spines) it is still able to process food through the Crassulacean Acid Metabolism (CAM) method.
The spine of a cactus has essentially been "modified" to cope with the photosynthesis process; ribs and tubercles in a cactus stem allow the stem to expand and contract to store water as available. The globular shape of cacti helps to minimize surface area but maximize storage capacity for water, an essential feature for the hot, dry climate. The thick, waxy skin of a cactus also helps to reduce water loss. The stomata of a cactus are contained in the skin.
Cacti open their stomata at night to take in carbon dioxide for processing the next day through the Crassulacean Acid Method in order to further minimize potential water loss; the next day, the cactus breaks down the carbon dioxide (stored as malic acid the night before), resulting in the final production of carbohydrates for the plant.
Photosynthesis in Cacti
Cacti are complex plant structures in comparison to regular plants and the process of photosynthesis that they carry out through the Crassulacean Acid Metabolism method is far more complex than described here. However, you can see from this brief introduction that cacti have developed a system of their own in order to carry out the vital life function of photosynthesis.
References:
- Cactus Museum website, Cactus Survival, accessed January 3, 2012
- School of Biological Sciences at the University of Texas website, Cactus Spines, accessed January 3, 2012
Sharon Falsetto - Sharon Falsetto is a business owner, certified clinical aromatherapist & professional writer with a life-long interest in plants.
