Saguaro
The saguaro is a tree-like cactus species in the monotypic genus Carnegiea that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains and Imperial County areas of California. Saguaro typically grow at elevations ranging from sea level to 4,500', although they may be found at up to 5,000'. The saguaro blossom is the state wildflower of Arizona. Its scientific name is given in honor of Andrew Carnegie. In 1933, Saguaro National Park, near Tucson, Arizona, was designated to help protect this species and its habitat.
Saguaros have a relatively long lifespan, often exceeding 150 years. They may grow their first side arm around 75–100 years of age, but some never grow any arms. Arms are developed to increase the plant's reproductive capacity, as more apices lead to more flowers and fruit. A saguaro can absorb and store considerable amounts of rainwater, visibly expanding in the process, while slowly using the stored water as needed. This characteristic enables the saguaro to survive during periods of drought. It is a keystone species, and provides food and habitat to a large number of species.
Saguaros have been a source of food and shelter for humans for thousands of years. Their sweet red fleshed fruits are turned into syrup by native peoples, such as the Tohono Oʼodham and Pima. Their ribs are used as building materials in the wood-poor deserts. The saguaro cactus is a common image in Mexican and Arizonan culture, and American Southwest films.
Description
The saguaro is a columnar cactus that grows notable branches, usually referred to as arms. Over 50 arms may grow on one plant, with one specimen having 78 arms. Saguaros grow from tall, and up to in diameter. They are slow growing, and routinely live 150 to 200 years. They are the largest cactus in the United States.The growth rate of this cactus is strongly dependent on precipitation; saguaros in drier western Arizona grow only half as fast as those in and around Tucson. Saguaros grow slowly from seed, and may be only tall after two years. Cuttings rarely root, and when they do, they do not go through the juvenile growth phase, which gives a different appearance. the National Register of Champion Trees listed the largest known living saguaro in the United States in Maricopa County, Arizona, measuring high with a girth of ; it has an estimated age of 200 years and survived damage in the 2005 Cave Creek Complex Fire. The tallest saguaro ever measured was an armless specimen found near Cave Creek, Arizona. It was in height before it was toppled in 1986 by a windstorm. Saguaros are stem succulents and can hold large amounts of water; when rain is plentiful and the saguaro is fully hydrated, it can weigh between.
| Height | Age |
| 9 | |
| 13 | |
| 27 | |
| 41 | |
| 83 | |
| 107 | |
| 131 | |
| 157 |
Saguaros have a very large root network that can extend up to, and long taproots of up to deep.
Saguaros may take between 20 and 50 years to reach a height of. Individual stomatal guard cells and medulla cells can live and function for as long as 150 years, possibly the longest living of all cells, except possibly nerve cells in some tortoises.
As a cactus, it uses crassulacean acid metabolism photosynthesis, which confers high levels of water-use efficiency. This allows the saguaro to transpire only at night, minimizing daytime water loss.
A saguaro without arms is called a "spear".
Some saguaros grow in rare formations called a cristate, or "crested" saguaro. This growth formation is believed to be found in one in roughly 10,000 saguaros, with 2,743 known crested saguaros documented. The crest formation, caused by fasciation, creates a seam of abnormal growth along the top or top of the arm of the saguaro.
Ribs
Inside the saguaro, many "ribs" of wood form something like a skeleton, with the individual ribs being as long as the cactus itself and up to a few centimeters in diameter. The rib wood itself is also relatively dense, with dry ribs having a solid density around, which made the ribs useful to indigenous peoples as a building material. While the ribs of dead plants are not protected by the Arizona native plant law, the Arizona Department of Agriculture has released a memo discussing when written permission is needed before harvesting them because of the importance of the decomposition of cactus remains in maintaining desert soil fertility.The composition of the ribs is similar to that of hardwoods.
Spines
The spines on a saguaro are extremely sharp and can grow to long, and up to per day. When held up to the light or bisected, alternating light and dark bands transverse to the long axis of spines are visible. These bands have been correlated to daily growth. In columnar cacti, spines almost always grow in areoles that originate at the apex of the plant. A spine stops growing in its first season. Areoles are moved to the side and the apex continues to grow upward. Thus, older spines are toward the base of a columnar cactus and newer spines are near the apex. A 2007 study examined the relationship of carbon and oxygen isotope ratios in the tissues of spines of an individual to its climate and photosynthetic history.The spines may cause significant injury to animals; one paper reported that a bighorn sheep skull had been penetrated by a saguaro spine after the sheep collided with a saguaro. They can also cause severe injury to humans, being as sharp and nearly as strong as steel needles. Their long, unbarbed nature means that partially embedded spines can be easily removed, but their relative length can complicate injuries. The spines can puncture deeply, and if broken off, can leave splinters of spine deep in the tissue that can be difficult to remove. Fully embedded spikes are also difficult to remove. Such injuries do not usually result in infection, though, as the cactus spines are generally aseptic. However, spines that remain embedded may cause inflammatory granuloma.
Flowers
The white, waxy flowers appear in April through June, opening well after sunset and closing in midafternoon. They continue to produce nectar after sunrise. Flowers are self-incompatible, thus requiring cross-pollination. Large quantities of pollen are required for complete pollination because many ovules are present. This pollen is produced by the extremely numerous stamens, which in one notable case in a single flower. A well-pollinated fruit contains several thousand tiny seeds.Pollination is considered relatively generalized in that multiple species can produce effective pollination when some populations are excluded. Main pollinators are honey bees, bats, and white-winged doves. In most, but not all studies, diurnal pollinators contributed more than nocturnal ones. Honey bees were the greatest contributors. Other diurnal pollinators are birds such as Costa's hummingbird, the black-chinned hummingbird, the broad-billed hummingbird, the hooded oriole, Scott's oriole, the Gila woodpecker, the gilded flicker, the verdin, and the house finch according to studies that examined the relative contributions of diurnal pollinators.
The primary nocturnal pollinator is the lesser long-nosed bat, feeding on the nectar. Several floral characteristics are geared toward bat pollination : nocturnal opening of the flowers, nocturnal maturation of pollen, very rich nectar, position high above ground, durable blooms that can withstand a bat's weight, and fragrance emitted at night. Claw marks on the flower indicate pollination by a bat.
Flowers grow long, and are open for less than 24 hours. Since they form only at the top of the plant and the tips of branches, saguaros growing numerous branches is reproductively advantageous. Flowers open sequentially, with plants averaging four flowers open per day over a bloom period lasting a month. In Southern Arizona, saguaros begin flowering around May 3 and peak on June 4. A decline in bat populations causes more daytime flower openings, which favors other pollinators.
Fruit
The ruby red fruits are long and ripen in June, each containing around plus sweet, fleshy connective tissue.The fruits are often out of reach and are harvested using a pole long, to the end of which cross-pieces, which can be made of saguaro rib, catclaw, or creosote bush, are attached. This pole is used to hook the fruits or knock them free.
Saguaro seeds are small and short-lived. Although they germinate easily, predation and lack of moisture prevent all but about 1% of seeds from successful germination. Seeds must wait 12–14 months before germination; lack of water during this period drastically reduces seedling survival. The existence of nurse plants is critical to seedling establishment. Palo verde trees and triangle bursage represent important nurse species. They act by regulating temperature extremes, increasing soil nutrients, and reducing evapotranspiration, among others. While nurse plants reduce summer temperature maxima by as much as, they are more important in raising winter minimum temperatures, as extended frosts limit the range of saguaros.
Native Americans of the Southwest would make bread from the ground seeds of saguaro.