The white, waxy flowers appear in April through June, opening well after sunset and closing in midafternoon. However, spines that remain embedded may cause inflammatory granuloma. Such injuries do not usually result in infection, though, as the cactus spines are generally aseptic. Fully embedded spikes are also difficult to remove. The spines can puncture deeply, and if broken off, can leave splinters of spine deep in the tissue that can be difficult to remove. Their long, unbarbed nature means that partially embedded spines can be easily removed, but their relative length can complicate injuries. They can also cause severe injury to humans, being as sharp and nearly as strong as steel needles. 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. 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). Thus, older spines are toward the base of a columnar cactus and newer spines are near the apex. Areoles are moved to the side and the apex continues to grow upward. A spine stops growing in its first season. In columnar cacti, spines almost always grow in areoles that originate at the apex of the plant. These bands have been correlated to daily growth. When held up to the light or bisected, alternating light and dark bands transverse to the long axis of spines are visible. The spines on a saguaro are extremely sharp and can grow to 7 cm (3 in) long, and up to 1 mm ( 1⁄ 32 in) per day. The composition of the ribs is similar to that of hardwoods. 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 rib wood itself is also relatively dense, with dry ribs having a solid density around 430 kg/m 3 (27 lb/cu ft), which made the ribs useful to indigenous peoples as a building material. 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 crest formation, caused by fasciation, creates a seam of abnormal growth along the top or top of the arm of the saguaro. This growth formation is believed to be found in one in roughly 10,000 saguaros, with 2743 known crested saguaros documented. Some saguaros grow in rare formations called a cristate, or "crested" saguaro. Ī saguaro without arms is called a "spear". This allows the saguaro to only transpire at night, minimizing daytime water loss. Īs a cactus, it uses crassulacean acid metabolism photosynthesis, which confers high levels of water-use efficiency. 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. Saguaros may take between 20 and 50 years to reach a height of 1 m (3 ft 3 in). 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. ![]() ![]() Įstimated age of Saguaros based on their height. 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 1,500 and 2,200 kg (3,200 and 4,800 lb). ![]() It was 78 ft (23.8 m) in height before it was toppled in 1986 by a windstorm. The tallest saguaro ever measured was an armless specimen found near Cave Creek, Arizona. Since 2014, the National Register of Champion Trees listed the largest known living saguaro in the United States in Maricopa 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 2005 Cave Creek Complex Fire. Cuttings rarely root, and when they do, they do not go through the juvenile growth phase, which gives a different appearance. Saguaros grow slowly from seed, and may be only 6.4 mm ( 1⁄ 4 in) tall after two years. 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.
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