Saguaro

Thesaguaro(/səˈ(ɡ)wɑːroʊ/sə-(G)WAR-oh,Spanish:[saˈɣwaɾo];Carnegiea gigantea) is a tree-likecactusspeciesin themonotypicgenusCarnegieathat can grow to be over 12 meters (40 feet) tall. It is native to theSonoran DesertinArizona, the Mexican state ofSonora, and theWhipple MountainsandImperial Countyareas of California. The saguaro blossom is thestate wildflowerof Arizona. Its scientific name is given in honor ofAndrew Carnegie. In 1933,Saguaro National Park, nearTucson, 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 moreapiceslead to moreflowersand 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 akeystone 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 theTohono OʼodhamandPima. 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.
The saguaro is a columnarcactusthat grows notablebranches, usually referred to as arms. Over 50 arms may grow on one plant, with one specimen having 78 arms.Saguaros grow from 3–16 m (10–52 ft) tall, and up to 75 cm (30 in) 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 onprecipitation; saguaros in drier western Arizona grow only half as fast as those in and aroundTucson. Saguaros grow slowly from seed, and may be only6.4 mm (1⁄4in) 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.Since 2014,theNational Register of Champion Treeslisted the largest known living saguaro in the United States inMaricopa County, Arizona, measuring 13.8 m (45 ft 3 in) high with a girth of 3.1 m (10 ft 2 in); it has an estimated age of 200 years and survived damage in the 2005Cave Creek Complex Fire.The tallest saguaro ever measured was an armless specimen found nearCave Creek, Arizona. It was 78 ft (23.8 m) in height before it was toppled in 1986 by a windstorm.Saguaros arestem succulentsand can hold large amounts of water; when rain is plentiful and the saguaro is fully hydrated, it can weigh between 1,500 and 2,200 kg (3,200 and 4,800 lb).
Saguaros have a very large root network that can extend up to 30 m (100 ft), and long taproots of up to 1 m (3 ft 3 in) deep.
Saguaros may take between 20 and 50 years to reach a height of 1 m (3 ft 3 in).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 usescrassulacean acid metabolismphotosynthesis, which confers high levels ofwater-use efficiency. This allows the saguaro totranspireonly 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 byfasciation, creates a seam of abnormal growth along the top or top of the arm of the saguaro.
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 430 kg/m(27 lb/cu ft),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, theArizona Department of Agriculturehas 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 ofhardwoods.
The spines on a saguaro are extremely sharp and can grow to 7 cm (3 in) long,and up to1 mm (1⁄32in) 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 oxygenisotoperatios in the tissues of spines of an individual to its climate andphotosynthetichistory (acanthochronology).
The spines may cause significant injury to animals; one paper reported that abighorn sheepskull 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 generallyaseptic. However, spines that remain embedded may cause inflammatorygranuloma.
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 areself-incompatible, thus requiring cross-pollination.Large quantities of pollen are required for complete pollination because manyovulesare present. This pollen is produced by the extremely numerous stamens, which in one notable casetotaled3482in 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. Mainpollinatorsarehoney bees, bats, andwhite-winged doves. In most, but not all studies,diurnalpollinators contributed more thannocturnalones. Honey bees were the greatest contributors. Other diurnal pollinators are birds such asCosta's hummingbird, theblack-chinned hummingbird, thebroad-billed hummingbird, thehooded oriole,Scott's oriole, theGila woodpecker, thegilded flicker, theverdin, and thehouse finchaccording to studies that examined the relative contributions of diurnal pollinators.
The primary nocturnal pollinator is thelesser long-nosed bat, feeding on thenectar. 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 8.6–12.4 cm (3.4–4.9 in) 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.
The ruby red fruits are6 to 9 cm (2+1⁄2to3+1⁄2in) long and ripen in June, each containing around2000seeds,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) 4.5 to 9 m (15 to 30 ft) long, to the end of which cross-pieces, which can be made of saguaro rib,catclaw, orcreosote 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 ofnurse plantsis critical to seedling establishment.Palo verde treesandtriangle bursagerepresent important nurse species. They act by regulating temperature extremes, increasing soil nutrients, and reducingevapotranspiration, 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.
Native American Indians of the Southwest would make bread from the ground seeds of saguaro.
The saguarogenomeis around 1 billionbase pairslong.Sequencinghas revealed that the genome of the saguaro'schloroplastis the smallest known among nonparasitic flowering plants. Like several other highly specialized plant taxa, such as the carnivorousGenliseaand parasiticCuscuta, the saguaro has lost thendhplastid genes, which codes for production ofNADPH dehydrogenasepathway, but unlike those taxa, the saguaro remains fullyautotrophic; 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 11ndhgenes remain in theplastid. The genes appear to have been copied to thenuclear DNAandmitochondrial 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 thendhgenes have been taken on by another pathway.
Carnegiea giganteais the only species in the monotypic genusCarnegiea.The first description of the species was made byWilliam H. Emoryin 1848, during his surveys along the pre-Gadsden PurchaseUnited States-Mexican border.This description allowed cactus expertGeorge Engelmannto formally name it, during his work on theUnited States and Mexican Boundary Survey, published in 1859.The next major taxonomic treatment came fromThe Cactaceae, the seminal work on cactus byNathaniel Lord BrittonandJoseph Nelson Rose.
WhattribeCarnegiea giganteabelongs to is a matter of taxonomic dispute. A molecular analysis of the cactus family in 2010 placed the saguaro in theEchinocereinae.TheARSGermplasm Resources Information Networkplaces it in theEchinocereeae.
The generic name honors businessman and philanthropistAndrew Carnegie.Thespecific epithetgigantearefers to its formidable size.
The Saguaro isendemicto theSonoran Desertand is found primarily in westernSonorain Mexico, and in westernArizonain 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.No confirmed specimens of wild saguaros have been found anywhere inNevada,New Mexico,Texas,Colorado,Utah, nor in the high deserts of northern Arizona.The northern limits of their range are theHualapai Mountainsin Arizona.They are the northernmost columnar cacti in the Americas.
The saguaro is akeystone 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.
The saguaro provides voluminous amounts of pollen, nectar, and fruits.The fruits are eaten by thewhite-winged doveand ants, so that seeds rarely escape to germinate.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.
Gila woodpeckersandgilded flickerscreate holes in the cactus to make nests, which are later used by other birds, such aself owls,purple martins, andhouse 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 createscallustissue on the wound. When the saguaro dies and its soft flesh rots, the callus remains as a so-calledsaguaro boot, which was used by natives for storage.
Gila woodpeckers (Melanerpes uropygialis) create new nest holes each season rather than reuse the old ones, leaving convenient nest holes for other birds, such as elf owls,tyrant flycatchers, andwrens.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, abald eaglewas found nesting in a saguaro for the first time since 1937.
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.
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 10 acres (4 hectares) 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 230 kg (500 lb), fell onto him, crushing him and his car. The trunk of the cactus then also fell on him.TheAustin Lounge Lizardswrote the song "Saguaro" about this death.
Contrary to published statements,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 asbuffelgrassandSahara 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 afire return intervalgreater 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 changemay 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.
The utility of the saguaro is well known toNative Americanssuch as theTohono O'odham,Pima, andSeripeoples, who still use nearly every part of the plant.The fruit and seeds are edible,being consumed fresh and dried, and made into preserves and drinks.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 Tohono O'odham begin their harvest in June. A pair of saguaro ribs, about 6 m (20 ft) long, are bundled together to make a harvesting tool called akuibit. The Tohono O'odham traditionally reduce the freshly harvested fruit into a thick syrup through several hours of boiling, as the fresh fruit does not keep for long. Four kilograms (9 pounds) of fruit will yield about1 liter (1⁄4U.S. gallon) of syrup. Copious volumes of fruit are harvested; an example harvest in 1929 yielded 45,000 kg (99,000 lb) among 600 families.At the end of the harvest, each family would contribute a small amount of syrup to a communal stock that would be fermented by the medicine man. This was cause for rainmaking celebrations: Stories would be told, there was much dancing, and songs would be sung. Each man would drink some of the saguaro wine. The resulting intoxicated state was seen as holy, and any dreams it brought on were considered portentous.
The saguaro features prominently in indigenous folklore and religions.Reports of saguaro use date back to theCoronadoexpeditions of 1540–1542, which noted its use in winemaking.
Arizona made the saguaro blossom its territorial flower on March 13, 1901, and on March 16, 1931, it became the state flower.
The saguaro is often used as an emblem in commercials and logos that attempt to convey a sense of theSouthwest. Notably, no naturally occurring saguaros are found within 400 kilometers (250 miles) ofEl Paso, Texas, but the silhouette is found on the label ofOld El Pasobrand products.Though the geographic anomaly has lessened in recent years,Western films once enthusiastically placed saguaros in theMonument Valleyof Arizona (north of their native range), as well as New Mexico, Utah, and Texas.
America West Airlines, and laterU.S. Airwaysafter 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.