Xerophyte

Trunk

Columnar, green, 30-75 cm in diameter, unbranched, erect, and straight with (on older plants) one to several branches originating 2-3 m above the base. Stem tissue turning black when cut or injured. The vertical ribs enable Carnegiea stems to expand as moisture is absorbed and to contract as it is used.

Seeds

Obovoid, 1,8-2,1 mm long, dark red-brown to blackish, shiny, nearly smooth, and edible.Chromosome number n = 11.

Phenology

Flowers appear from late April to early June. Fruits ripen from late May until mid July while stems grow mostly during rainy periods in July, August, and September.

Roots

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 giganteaSN|6374]]SN|6374]] 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.

Note

Saguaro and cardon (Pachyrereus pringlei), the two largest cacti in the Sonoran Desert, often occur together in western Sonora. Saguaros generally initiate branches higher off the ground and the mature stems are green rather than glaucous. Pachyrereus pringlei is a stouter, more massive plant that branches closer to the ground and has fewer (10-15) vertical ribs. The young plants, however, may be difficult to distinguish.

Flowers

White and showy 8,5-12,5 cm long, 5-6 cm in across, opening in late afternoon and remaining open until the midday or later of the following day depending on temperature, then closing permanently, funnelform to bell-shaped, with creamy white petals around a dense group of yellow stamens. Pericarpel and floral tube 6-10 cm long, covered with many distinct scales, extending down and clasping, and felted areoles. Though normally found at the end of the main trunk and arms just below the stem tips, flowers may also occur down the sides of the plant. First buds emerging on south or south-west side of the stems. Flowers will continue to be produced throughout a saguaro's lifetime. A stem might produce more than 100 flowers at a time! The saguaro has more stamens per flower than any other cactus flower. To set fruit, flowers must receive pollen from another plant or from flowers on another arm of the same plant

Fruits

Egg shaped, with scales, spine-less (or occasionally with a few bristly spines), 5-7,5(-10) cm long, 2,5–4,4 cm in diameter, fleshy, green, red or purple at maturity, dehiscent and splitting open, along three or four vertical lines, exposing the bright red interior, the pulp juicy, bright red, sweet, and edible.