Carnegiea gigantea

The saguaro is a columnar cactus that grows notable branches, usually referred to as arms. As many as 49 arms may grow on one plant. They grow from 3–16 m (9.8–52.5 ft) tall, and up to 75 cm (30 in) in diameter. They are slow growing, but routinely live 150 to 200 years. They are the largest cactus in the United States.The growth rate of saguaros 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 only be 0.25 in (0.64 cm) tall after 2 years. Cuttings rarely root, and when they do, they do not go through the juvenile growth phase, which gives a different appearance. Since 2014, the National Register of Champion Trees listed the largest known living saguaro in the United States in Maricopa County, Arizona, measuring 45.3 ft (13.8 m) high with a girth of 10 ft (3.1 m); 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 78 ft (23.8 m) in height before it was toppled in 1986 by a windstorm. They are stem succulents and can hold large amounts of water; when rain is plentiful and the saguaro is fully hydrated, it can weigh between 3,200 and 4,800 lb (1,500 and 2,200 kg).Saguaros have a very large root network that can extend up to 30 m (98 ft), and long taproots of up to 1 m (3.3 ft) deep.Saguaros may take between 20 and 50 years to reach a height of 1 m (3.3 ft).As a cactus, it uses crassulacean acid metabolism photosynthesis, which confers high levels of water-use efficiency. This allows the saguaro to only transpire 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 2743 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.
RibsEdit
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 inches in diameter. The rib wood itself is also relatively dense, with dry ribs having a solid density around 430 kg/m, 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 the decomposition of cactus remains in maintaining desert soil fertility.The composition of the ribs is similar to that of hardwoods.
SpinesEdit
  Saguaro spines
The spines on a saguaro are extremely sharp and can grow up to 1 mm (0.039 in) 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. Studies are underway to examine the relationship of carbon and oxygen isotope ratios in the tissues of spines of an individual to its climate and photosynthetic history (acanthochronology).Spines grow to 7 cm (2.8 in) long.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, leaving splinters of spine deep in the tissue, which 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.
FlowersEdit
  Saguaro 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 totaled 3,482 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 (chiropterophily): 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 3.4–4.9 in (8.6–12.4 cm) 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 open flowers a 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.
FruitEdit
  House finch perched atop fruits at the tip of a saguaro
The ruby red fruits are 2.4 to 3.5 in (6 to 9 cm) long and ripen in June, each containing around 2,000 seeds, plus sweet, fleshy connective tissue.The fruits are often out of reach and are harvested using a pole (made of two or three saguaro ribs) 15 to 30 ft (4.5 to 9 m) 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 18 °C (32 °F), they are more important in raising winter minimum temperatures – as extended frosts limit the range of saguaros.
GenomeEdit
The saguaro genome is around 1 billion base pairs long. Sequencing has revealed that the genome of the saguaro's chloroplast is the smallest known among nonparasitic flowering plants. Like several other highly specialized plant taxa, such as the carnivorous Genlisea and parasitic Cuscuta, the saguaro has lost the ndh plastid gene, which codes for production of NADPH dehydrogenase pathway, but unlike those taxa, the saguaro remains fully autotrophic; i.e. it does not eat or steal part of its food. The saguaro is remarkable for the scale and completeness of gene loss; essentially no traces of the 11 ndh genes remain in the plastid. The genes appear to have been copied to the nuclear DNA and mitochondrial DNA, but those copies are non-functional. How the saguaro thrives in a high stress environment without working copies of this fairly important gene remains unknown, but it is possible that the functions of the ndh genes have been taken on by another pathway.

Water sparingly, allowing the mix to nearly dry out between watering.

Carnegiea Gigantea

Carnegiea gigantea

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