Saguaro (Carnegiea gigantea)

Description

The saguaro (/səˈwɑːroʊ/, Spanish pronunciation: [saˈɣwaɾo]) (Carnegiea gigantea) is an arborescent (tree-like) cactus species in the monotypic genus Carnegiea, which can grow to be over 40 feet (12 m) 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. The saguaro blossom is the state wildflower of Arizona. Its scientific name is given in honor of Andrew Carnegie. In 1994, Saguaro National Park, near Tucson, Arizona, was designated to help protect this species and its habitat. The image of the saguaro is indelibly linked with that of the American Southwest, especially in western films. The common name saguaro came into the English language through the Spanish language, originating in the Mayo language. 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, never from cuttings, and grow to be over 40 feet (12.2 metres) in height. The largest known living saguaro is the Champion Saguaro growing in Maricopa County, Arizona, measuring 45.3 feet (13.8 metres) high with a girth of 10 feet (3.1 metres). The tallest saguaro ever measured was an armless specimen found near Cave Creek, Arizona. It was 78 feet (23.8 metres) in height before it was toppled in 1986 by a windstorm. A saguaro is able to 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. When rain is plentiful and the saguaro is fully hydrated it can weigh between 3200-4800 pounds. 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 non-parasitic flowering plants. The spines on a saguaro, less than two meters in height, rapidly grow up to a millimeter per day. When held up to the light or bisected, alternating light and dark bands transverse to the long axis of spines can be seen. These transverse bands have been correlated to daily growth. In columnar cacti, spines almost always grow in areoles which 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 upwards. Thus, older spines are towards 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).