A cactus is a member of the plant family Cactaceae[a], which has about 127 genera and about 1750 recognized species. Cactaceae belongs to the order Caryophyllales. [4] The Latin word “cactus” is derived from the Ancient Greek word “kktos,” which Theophrastus first used to refer to a spiky plant whose identify is currently unknown. [5] There are many different sizes and shapes of cacti. Most cactus reside in settings that experience at least some drought, despite the fact that some species can tolerate fairly humid situations. Many of them can even be found in the Atacama Desert, one of the driest places on Earth, where they exist in extremely dry circumstances. Cacti have developed a variety of adaptations to conserve water as a result. As an illustration, nearly all cacti are succulents, which means that their swollen, fleshy sections are designed to store water. Unlike many other succulents, most cacti only have a stem where this crucial process occurs. The majority of cacti species no longer have actual leaves; instead, they only have spines, which are heavily modified leaves. Spines help limit water loss by slowing air movement around the cactus and offering some shade, in addition to protecting it from herbivores. Photosynthesis is performed by cacti’s expanded stems in the lack of real leaves. Except for Rhipsalis baccifera, which also grows in Africa and Sri Lanka, all of the Americas, from Patagonia in the south to sections of western Canada in the north, are home to cacti.
Areoles, a type of greatly shortened branch, are specialized structures that create cactus spines. Cacti can be identified by their areoles. Areoles also produce multipetalled, tubular blooms in addition to spines. Because many cacti have extended dormant periods and short growing seasons, they may respond fast to any rainfall. This is made possible by their large but shallow root systems, which swiftly absorb any water that reaches the ground surface. Because cactus stems are frequently ribbed or fluted, they can easily stretch and contract to quickly absorb water after rain and then hold onto it during protracted droughts. The majority of cacti use a unique process called “crassulacean acid metabolism” (CAM) as part of photosynthesis, similar to other succulent plants. Unlike photosynthesis, which occurs during the day, transpiration—during which carbon dioxide enters the plant and water escapes—occurs at night. The plant converts the carbon dioxide it absorbs into malic acid and stores it there until daybreak, when it is solely used for photosynthesis. The cooler, more humid nighttime hours are when transpiration occurs, which greatly reduces water loss.
The globe-shaped stems of many smaller cacti combine the maximum volume of water storage with the smallest surface area of transpiration loss. The largest[b] free-standing cactus is Pachycereus pringlei, which reaches a maximum height of 19.2 m (63 ft)[7], while Blossfeldia liliputiana has the lowest diameter at maturity, measuring just around 1 cm (0.4 in). [8] During a downpour, a mature saguaro (Carnegiea gigantea) is believed to be capable of soaking up 200 US gallons (760 l; 170 imp gal) of water. [9] Only a few species look significantly like the rest of the family. Plants belonging to the genera Leuenbergeria, Rhodocactus, and Pereskia resemble nearby trees and bushes, at least on the surface. They have enduring leaves and, as they age, stems covered with bark. Despite their appearance, they are recognized as cacti by their areoles and have numerous water-saving adaptations. Leuenbergeria is thought to be very closely related to the original species from which all cacti descended. Other cacti develop as forest climbers and epiphytes in tropical areas (plants that grow on trees). Their stems often have fewer or even no spines and are flattened, almost leaf-like in appearance, like the well-known Christmas or Thanksgiving cactus (in the genus Schlumbergera).
Many types of cacti are produced as beautiful plants, while others are raised for fodder or forage, and yet others are utilized as food (particularly their fruit). An bug that lives on some cactus produces cochineal.
Many succulent plants, both in the Old and New Worlds, have spiky stems, including some members of the Euphorbiaceae (euphorbias), which is why they are frequently mistakenly called “cactus.”
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