Giant Saguaro Cactus, Carnegiea gigantea (Occasionally misspelled "Carnegia"), long popular because of its immense size and unique architecture is, perhaps, the more famous of all cacti. It is the most well-known of a group of spectacular columnar cacti from the Sonoran Desert that includes the cardons (Pachycereus pringlei), the organ-pipe cactus (Stenocereus thurberi) and senita (Lophocereus schottii).

Root: Has a shallow root system with small roots radiating out the height of the cactus and the some. No taproot.
Habit. It is a large, treelike, columnar, perennial succulent that has one or more founded arms from a single, thick trunk. It usually attains the height of about 9 metres, but exceptionally it can tower as high as 16 metres and weighing more than 10 tons, dwarfing every other living thing in the desert. The morphological behaviour of Carnegiea gigantea is also quite remarkable. It shows a marked dimorphism. In its juvenile (or sterile) stage it forms a green, cylindrical solitary columnar stem up to 3 metres tall, mostly with 11-15 stem ribs. The areoles are separate, spaced about 2-3 cm apart on the ribs, with 15-30, stout, rigid spines, grey to blackish, diverging, straight the longer central of which (3,5-) 5,5-11 cm long and (0,8) 1,1-2,3 mm in diameter, these areoles not producing flowers. In mature (Adult or fertile) stage it start branching forming stems with shallow, blunt ribs often 19-25. Areoles closely set with flexible, bristly spines 2,2-3 cm long and 0,3-0,4 mm, producing flowers. First branches usually arising in the region of transition between the juvenile and mature part, the branches fertile. The flowers and fruits are found only on the adult bristly branches, high enough to escape the grazing of herbivores.