Parts of a Cactus

Cactus are a tropical plant that produces sharp thorns, sharp stems, and spines. The United States imports and exports cactus.Cacti are plants succulents that have managed to adapt to an arid environment, where very few animals and plants coexist. Its roots develop on a sandy soil, with very few nutrients. Thus, its parts are so striking, because they do not resemble those of other plants.From them arise the thorns and flowers of the cactus. They are shaped like a small pad, and are located on the ribs of the same. In each of them there are two types of spines: the radial ones, which are small and numerous, and the central ones, which usually appear in number from 1 to 3 and are longer.They are modified leaves; in fact, the correct term is foliar thorn (foliar means relative to the leaves). These have different functions: protect from the sun and herbivorous predators, direct the water towards the body of the cactus and prevent the evaporation of the water.

Cactus

Cacti occur in a wide range of shapes and sizes. Although some species live in quite humid environments, most cacti live in habitats subject to at least some drought. Many live in extremely dry environments, even being found in the Atacama Desert, one of the driest places on earth. Cacti show many adaptations to conserve water. Almost all cacti are succulents, meaning they have thickened, fleshy parts adapted to store water. Unlike many other succulents, the stem is the only part of most cacti where this vital process takes place. Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. As well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of leaves, enlarged stems carry out photosynthesis. Cacti are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north—except for Rhipsalis baccifera, which also grows in Africa and Sri Lanka.

Cactus spines are produced from specialized structures called areoles, a kind of highly reduced branch. Areoles are an identifying feature of cacti. As well as spines, areoles give rise to flowers, which are usually tubular and multipetaled. Many cacti have short growing seasons and long dormancies, and are able to react quickly to any rainfall, helped by an extensive but relatively shallow root system that quickly absorbs any water reaching the ground surface. Cactus stems are often ribbed or fluted, which allows them to expand and contract easily for quick water absorption after rain, followed by long drought periods. Like other succulent plants, most cacti employ a special mechanism called "crassulacean acid metabolism" (CAM) as part of photosynthesis. Transpiration, during which carbon dioxide enters the plant and water escapes, does not take place during the day at the same time as photosynthesis, but instead occurs at night. The plant stores the carbon dioxide it takes in as malic acid, retaining it until daylight returns, and only then using it in photosynthesis. Because transpiration takes place during the cooler, more humid night hours, water loss is significantly reduced. (Source: en.wikipedia.org)