Cacti vs Succulents
The main problem that plants growing in dry and hot environments face is the excessive water loss due to transpiration. An important adaptation shown by cacti and other succulents to overcome this problem is their Crassulacean acid metabolism (CAM). CAM plants open their stomata at night capturing carbon dioxide and close them during the day when it is hot and dry. This reduces transpiration in the plant to a greater extent.
Cacti
Cacti belong to the family Cactaceae. Their morphology is different from other normal plants. That is an adaption to conserve water in dry and hot environments. In cacti, the leaves are modified to form spines and the stem is modified for photosynthesis. There are different types of cacti. The tallest cactus is Pachycereus pringlei. It is about 19 meters tall. The smallest cactus is Blossfeldia liliputiana. The large flowers of cacti arise from special structures called areoles. Cacti are succulent plants. In most cacti leaves are modified into spines. The spines can absorb moisture in the air to some extent. It hardly loses the absorbed water. The spines perform another important function. They trap moisture and create a moisture layer near the surface of the cactus stem. This helps the plant to reduce transpiration and thus conserve some water. Spines can also protect the plant from herbivores. The spines develop from areoles. Areoles are identical to the nodes on the plants. Only few cacti possess leaves, and those are also very small and they fall off soon to reduce transpiration. Some ancestral cacti have large leaves, and they do not have succulent stems. In addition to the photosynthesis cacti stems also store water. The stems are usually enlarged to store water. Most of the time cacti have a waxy layer on the stems, and that is present to reduce transpiration of water and conserve water. As the plant contains a lot of water, the parts of the plant that gets separated from the plant can survive for a longer period. Then they can root when the rainy season comes. When considering the body shape of the cactus plant it is cylindrical. This shape reduces the surface area which receives sunlight. Cacti roots are not deeply rooted. They are close to the surface and are wide spread to collect maximum possible amount of water covering a larger area. This is a good adaptation to the rains, which are not frequent in those areas.
Succulents
Succulents are a type of plants that are adapted to hot and dry environments. They have the ability to retain water inside the plant. Succulents are able to store water in their stems, leaves and even in their roots. The plants that survive under unfavorable conditions due to rhizomes, corms, bulbs and tuberous roots can be categorized under succulents. The fleshy appearance of succulents is due to storage of water. This is known as succulence. In most succulents, leaves are absent or reduced. Even if resent they are very small leaves to reduce transpiration. Also, they reduce transpiration by reducing the number of stomata. In succulents, the stems are modified to carry out photosynthesis. Spines create a moisture layer around the plant reducing the water potential gradient and thus reducing transpiration. Roots are not deeply rooted, and they are near to the surface and wide spread to collect water even from very small rains. In addition, succulents possess a very thick cuticle, which is impervious to water.
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What is the difference between Cacti and Succulents? • All cacti are succulents, but not all succulents are cacti.
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