Saguaro

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. 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 . 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. 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. A well-pollinated fruit contains several thousand tiny seeds. 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. A decline in bat populations causes more daytime flower openings, which favors other pollinators. Fruit perched atop fruits at the tip of a saguaro 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 (made of two or three saguaro ribs) 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. Native Americans of the Southwest would make bread from the ground seeds of saguaro. Genome 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 genes, 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. == Taxonomy ==

Carnegiea gigantea is the only species in the monotypic genus Carnegiea. This description allowed cactus expert George Engelmann to formally name it, during his work on the United States and Mexican Boundary Survey, published in 1859. The next major taxonomic treatment came from The Cactaceae, the seminal work on cactus by Nathaniel Lord Britton and Joseph Nelson Rose. What tribe Carnegiea gigantea belongs to is a matter of taxonomic dispute. A molecular analysis of the cactus family in 2010 placed the saguaro in the Echinocereinae. The ARS Germplasm Resources Information Network places it in the Echinocereeae. The generic name honors businessman and philanthropist Andrew Carnegie. The specific epithet gigantea refers to its formidable size. == Etymology ==

The genus name Carnegiea honors industrialist Andrew Carnegie (1835-1919), whose Carnegie Institution established the Desert Botanical Laboratory in Tucson in 1903. The species epithet gigantea derives from the Greek root for giant, giga, due to the massive size of the cactus. Indigenous Names The O'odham peoples of the Northern Sonoran Desert know this species as Ha:san in their native language. Stemming from this native origin, it is thought that the term "Saguaro" is a Hispanized version brought on later by Spanish settlers. ==Distribution and habitat==

, Sonora. The Saguaro is endemic to the Sonoran Desert and is found primarily in western Sonora in Mexico, and in western Arizona in the US. There are only 30 known wild saguaros found in southeastern California. Elevation is a limiting factor to its environment, as the saguaro is sensitive to extended frost or cold temperatures. The northern limits of their range are the Hualapai Mountains in Arizona. The range of the saguaro is strongly correlated with low minimum temperature stress and low minimum VPD. == Ecology ==

The saguaro is a keystone species, and provides food, shelter, and protection to hundreds of other species. Every stage of the saguaro's life sustains a significant number of species, from seedling to after its death. As food for wildlife The saguaro provides voluminous amounts of pollen, nectar, and fruits. White-winged doves are important pollinators, visiting blooms more often than any other bird species. For desert white-winged doves, 60% or more of their diet is saguaro-based. Their breeding cycle coincides with that of the saguaro blooming. Nests Gila woodpeckers and gilded flickers create holes in the cactus to make nests, which are later used by other birds, such as elf owls, purple martins, and house finches. Gilded flickers excavate larger holes higher on the stem compared to Gila woodpeckers. The resulting nest cavity is deep, and the parents and young are entirely hidden from view. The saguaro creates callus tissue on the wound. When the saguaro dies and its soft flesh rots, the callus remains as a so-called saguaro boot, which was used by natives for storage. In recent years, early-breeding aggressive non-native birds have taken over the nests, to the detriment of elf owls that breed and nest later. In 2020, a bald eagle was found nesting in a saguaro for the first time since 1937. Carbon sequestration Saguaros transform significant amounts of the carbon in carbon dioxide into the mineral calcium carbonate when they die. Through the formation of a mineral, cacti transfer carbon from the earth's biological cycle to its geological cycle. This form of carbon sequestration is a terrestrial equivalent to oceanic sequestration by corals and shellfish. ==Conservation==

|alt= man standing next to a large Saguaro at Saguaro National Park Harming or vandalizing a saguaro in any manner, such as shooting them (sometimes known as "cactus plugging") is illegal by state law in Arizona. When houses or highways are built, special permits must be obtained to move or destroy any saguaro affected. Exceptions to this general understanding exist; for example, a private landowner whose property is or less, where the initial construction has already occurred, may remove a saguaro from the property. This is common when the cactus falls over in a storm, its location interferes with a house addition, or it becomes a potential hazard to humans. In 1982, a man was killed after damaging a saguaro. David Grundman was shooting and poking at a saguaro cactus in an effort to make it fall. An arm of the cactus, weighing , fell onto him, crushing him and his car. The trunk of the cactus then also fell on him. He was under the arm, and was shooting it with his friend. The Austin Lounge Lizards wrote the song "Saguaro" about this death. no law mandates prison sentences of 25 years for cutting a cactus down; however, it is considered a class-four felony with a possible 3-year, 9-month maximum sentence. Invasive species, such as buffelgrass and Sahara mustard, pose significant threats to the Sonoran Desert ecosystem by increasing the rate of fires. Buffelgrass outcompetes saguaros for water, and grows densely. It is also extremely flammable, but survives fire easily due to deep root systems. Saguaros did not evolve in an environment with frequent fires, thus are not adapted to fire survival. Most Sonoran desert ecosystems have a fire return interval greater than 250 years; buffelgrass thrives at fire return intervals of two to three years. This has led to the reshaping of the Sonoran Desert ecosystem and threatens the survival of the saguaro. Climate change may threaten saguaros and their ecosystems, as deserts are particularly susceptible to climate effects. Rising daytime and nighttime temperatures will reduce the water use efficiency of saguaros, forcing them to use more water and making them more likely to die during drought periods. ==Uses==

women gathering saguaro fruits, photo by Edward S. Curtis, 1907 Ethnobotany The utility of the saguaro is well known to Native Americans such as the Tohono O'odham, Pima, and Seri peoples, who still use nearly every part of the plant. The fruit and seeds are edible, The Tohono O'odham use long sticks to harvest the fruits, which are then made into a variety of products, including jams, syrups, and wine. • The seeds are ground into meal or eaten raw, but the raw seeds are mostly indigestible. They are also pressed for their oils. They also have minor use in the tanning of leather. In modern times, these uses have declined, and the seeds are now mainly used as chicken feed. The saguaro is often used as an emblem in commercials and logos that attempt to convey a sense of the Southwest. Notably, no naturally occurring saguaros are found within of El Paso, Texas, but the silhouette is found on the label of Old El Paso brand products. Though the geographic anomaly has lessened in recent years, Western films once enthusiastically placed saguaros in the Monument Valley of Arizona (north of their native range), as well as New Mexico, Utah, and Texas. America West Airlines, and later U.S. Airways after their merger in 2007, used the call sign "CACTUS" for radio communication on flights. America West was based in Phoenix, AZ, and "cactus" was chosen as a tribute to the saguaro cacti growing in the Phoenix area. ==Gallery==

File:Saguaro Sunset.jpg|Silhouette at sunset File:Crestedsaguaro.jpg|A crested saguaro File:Saguaro Cactus AZ.jpg|Saguaro towering over a man File:Saguaro5763.jpg|Mature five-armed in flower File:Saguaro-3.jpg|Snow-covered saguaro near Tucson File:Saguaro1a.jpg|Needles, Paradise Valley, Arizona File:Saguaroflowers.jpg|Flowers, Scottsdale, Arizona File:Dead saguaro1.jpg|The bare wooden ribs of a dead saguaro File:Grand-daddy, the largest saguaro.jpg|"Grand-daddy", the largest saguaro ever recorded, died in the early 1990s File:Saguaro Cactus With Desert Butte In Background At Springtime In AZ.jpg|Saguaro in blossom in springtime ==Footnotes==